This will create easily solved breakage on updates but
I figure it's best to pull the band aid off as early as possible

Standard library does this too. Unfortunate wish they just exposed it in the
standard library. Perhaps we can isolate the specific code we need later.

I'm just not good enough at assembly. I added tests to confirm that @wdvxdr's
implementation works correctly and matches the output of the basic masking loop.

Slower for some reason than just SIMD.

Also no dependency on cpu package is nice.

goos: windows
goarch: amd64
pkg: nhooyr.io/websocket
cpu: Intel(R) Core(TM) i5-9300H CPU @ 2.40GHz
Benchmark_mask/2/basic-8         	425339004	         2.795 ns/op	 715.66 MB/s
Benchmark_mask/2/nhooyr-8        	379937766	         3.186 ns/op	 627.78 MB/s
Benchmark_mask/2/gorilla-8       	392164167	         3.071 ns/op	 651.24 MB/s
Benchmark_mask/2/gobwas-8        	310037222	         3.880 ns/op	 515.46 MB/s
Benchmark_mask/3/basic-8         	321408024	         3.806 ns/op	 788.32 MB/s
Benchmark_mask/3/nhooyr-8        	350726338	         3.478 ns/op	 862.58 MB/s
Benchmark_mask/3/gorilla-8       	332217727	         3.634 ns/op	 825.43 MB/s
Benchmark_mask/3/gobwas-8        	247376214	         4.886 ns/op	 614.01 MB/s
Benchmark_mask/4/basic-8         	261182472	         4.582 ns/op	 872.91 MB/s
Benchmark_mask/4/nhooyr-8        	381830712	         3.262 ns/op	1226.05 MB/s
Benchmark_mask/4/gorilla-8       	272616304	         4.395 ns/op	 910.04 MB/s
Benchmark_mask/4/gobwas-8        	204574558	         5.855 ns/op	 683.19 MB/s
Benchmark_mask/8/basic-8         	191330037	         6.162 ns/op	1298.24 MB/s
Benchmark_mask/8/nhooyr-8        	369694992	         3.285 ns/op	2435.65 MB/s
Benchmark_mask/8/gorilla-8       	175388466	         6.743 ns/op	1186.48 MB/s
Benchmark_mask/8/gobwas-8        	241719933	         4.886 ns/op	1637.45 MB/s
Benchmark_mask/16/basic-8        	100000000	        10.92 ns/op	1464.83 MB/s
Benchmark_mask/16/nhooyr-8       	272565096	         4.436 ns/op	3606.98 MB/s
Benchmark_mask/16/gorilla-8      	100000000	        11.20 ns/op	1428.53 MB/s
Benchmark_mask/16/gobwas-8       	221356798	         5.405 ns/op	2960.45 MB/s
Benchmark_mask/32/basic-8        	61476984	        20.40 ns/op	1568.80 MB/s
Benchmark_mask/32/nhooyr-8       	238665572	         5.050 ns/op	6337.22 MB/s
Benchmark_mask/32/gorilla-8      	100000000	        12.09 ns/op	2647.28 MB/s
Benchmark_mask/32/gobwas-8       	186077235	         6.477 ns/op	4940.36 MB/s
Benchmark_mask/128/basic-8       	14629720	        80.90 ns/op	1582.19 MB/s
Benchmark_mask/128/nhooyr-8      	181241968	         6.565 ns/op	19497.98 MB/s
Benchmark_mask/128/gorilla-8     	68308342	        16.76 ns/op	7639.37 MB/s
Benchmark_mask/128/gobwas-8      	94582026	        12.97 ns/op	9872.11 MB/s
Benchmark_mask/512/basic-8       	 3921001	       305.6 ns/op	1675.55 MB/s
Benchmark_mask/512/nhooyr-8      	123102199	         9.721 ns/op	52669.11 MB/s
Benchmark_mask/512/gorilla-8     	32355914	        38.18 ns/op	13411.43 MB/s
Benchmark_mask/512/gobwas-8      	31528501	        37.80 ns/op	13544.37 MB/s
Benchmark_mask/4096/basic-8      	  491804	      2381 ns/op	1720.39 MB/s
Benchmark_mask/4096/nhooyr-8     	26159691	        46.98 ns/op	87187.73 MB/s
Benchmark_mask/4096/gorilla-8    	 4898440	       243.6 ns/op	16817.89 MB/s
Benchmark_mask/4096/gobwas-8     	 4336398	       277.2 ns/op	14776.40 MB/s
Benchmark_mask/16384/basic-8     	  113842	      9623 ns/op	1702.66 MB/s
Benchmark_mask/16384/nhooyr-8    	 8088847	       154.5 ns/op	106058.18 MB/s
Benchmark_mask/16384/gorilla-8   	 1282993	       933.6 ns/op	17549.90 MB/s
Benchmark_mask/16384/gobwas-8    	  997347	      1086 ns/op	15093.49 MB/s

We're about 4-5x faster then gorilla now.

Closes #297

Fixes https://github.com/nhooyr/websocket/issues/359

Closes #220 and #230

Closes #166

See https://github.com/nhooyr/websocket/issues/182

Closes #182

Closes #179

On average, we are 1.75x faster than both now 

goos: linux
goarch: amd64
pkg: nhooyr.io/websocket
Benchmark_mask/2/basic-8         	263923018	         4.55 ns/op	 439.76 MB/s
Benchmark_mask/2/nhooyr-8        	200203578	         6.00 ns/op	 333.32 MB/s
Benchmark_mask/2/gorilla-8       	241622557	         4.95 ns/op	 404.38 MB/s
Benchmark_mask/2/gobwas-8        	200392592	         6.05 ns/op	 330.69 MB/s
Benchmark_mask/3/basic-8         	207684956	         5.78 ns/op	 519.07 MB/s
Benchmark_mask/3/nhooyr-8        	169297215	         7.10 ns/op	 422.49 MB/s
Benchmark_mask/3/gorilla-8       	205775799	         5.81 ns/op	 516.23 MB/s
Benchmark_mask/3/gobwas-8        	165921662	         7.23 ns/op	 415.06 MB/s
Benchmark_mask/4/basic-8         	167034886	         7.18 ns/op	 557.30 MB/s
Benchmark_mask/4/nhooyr-8        	287656454	         4.30 ns/op	 931.11 MB/s
Benchmark_mask/4/gorilla-8       	166140434	         7.30 ns/op	 547.57 MB/s
Benchmark_mask/4/gobwas-8        	138138087	         8.73 ns/op	 458.20 MB/s
Benchmark_mask/8/basic-8         	121179904	         9.92 ns/op	 806.67 MB/s
Benchmark_mask/8/nhooyr-8        	199632992	         6.07 ns/op	1318.60 MB/s
Benchmark_mask/8/gorilla-8       	100000000	        10.8 ns/op	 739.65 MB/s
Benchmark_mask/8/gobwas-8        	157898031	         7.54 ns/op	1061.27 MB/s
Benchmark_mask/16/basic-8        	73648268	        16.5 ns/op	 971.56 MB/s
Benchmark_mask/16/nhooyr-8       	186871615	         6.38 ns/op	2506.61 MB/s
Benchmark_mask/16/gorilla-8      	72374540	        16.6 ns/op	 964.36 MB/s
Benchmark_mask/16/gobwas-8       	127698723	         9.36 ns/op	1709.99 MB/s
Benchmark_mask/32/basic-8        	40010325	        29.8 ns/op	1073.76 MB/s
Benchmark_mask/32/nhooyr-8       	168590156	         7.12 ns/op	4494.72 MB/s
Benchmark_mask/32/gorilla-8      	67282072	        17.7 ns/op	1808.59 MB/s
Benchmark_mask/32/gobwas-8       	120038877	         9.96 ns/op	3213.55 MB/s
Benchmark_mask/128/basic-8       	10134963	       118 ns/op	1082.74 MB/s
Benchmark_mask/128/nhooyr-8      	100000000	        11.8 ns/op	10852.23 MB/s
Benchmark_mask/128/gorilla-8     	45452385	        26.4 ns/op	4853.64 MB/s
Benchmark_mask/128/gobwas-8      	57188290	        20.8 ns/op	6153.80 MB/s
Benchmark_mask/512/basic-8       	 2707371	       442 ns/op	1159.38 MB/s
Benchmark_mask/512/nhooyr-8      	37049421	        32.4 ns/op	15785.82 MB/s
Benchmark_mask/512/gorilla-8     	19006171	        62.8 ns/op	8150.01 MB/s
Benchmark_mask/512/gobwas-8      	21394864	        55.8 ns/op	9169.49 MB/s
Benchmark_mask/4096/basic-8      	  346566	      3467 ns/op	1181.46 MB/s
Benchmark_mask/4096/nhooyr-8     	 5170425	       232 ns/op	17648.07 MB/s
Benchmark_mask/4096/gorilla-8    	 2963664	       405 ns/op	10105.59 MB/s
Benchmark_mask/4096/gobwas-8     	 2989596	       402 ns/op	10192.40 MB/s
Benchmark_mask/16384/basic-8     	   86671	     13833 ns/op	1184.38 MB/s
Benchmark_mask/16384/nhooyr-8    	 1332649	       889 ns/op	18436.40 MB/s
Benchmark_mask/16384/gorilla-8   	  763900	      1556 ns/op	10527.53 MB/s
Benchmark_mask/16384/gobwas-8    	  764034	      1553 ns/op	10548.60 MB/s
PASS
ok  	nhooyr.io/websocket	64.091s

Results from a 8 GB 8 core Haswell VM on GCP.

Much faster.

I changed my mind after #103 as browsers include a wasClean event to indicate
whether the connection was closed cleanly. From my tests, if a server using
this library prior to this commit initiates the close handshake, wasClean
will be false for the browser as the connection was closed before it could
respond with a close frame. Thus, I believe it's necessary to fully implement
the close handshake.

@stephenyama You'll enjoy this.

Subprotocols didn't work with WASM at all before.

Closes #121

The boys in the office hated it.

Highly unfortunate but makes sense as it seems confusing.