* all: freezer style syncing

core, eth, les, light: clean up freezer relative APIs

core, eth, les, trie, ethdb, light: clean a bit

core, eth, les, light: add unit tests

core, light: rewrite setHead function

core, eth: fix downloader unit tests

core: add receipt chain insertion test

core: use constant instead of hardcoding table name

core: fix rollback

core: fix setHead

core/rawdb: remove canonical block first and then iterate side chain

core/rawdb, ethdb: add hasAncient interface

eth/downloader: calculate ancient limit via cht first

core, eth, ethdb: lots of fixes

* eth/downloader: print ancient disable log only for fast sync

* freezer: implement split files for data

* freezer: add tests

* freezer: close old head-file when opening next

* freezer: fix truncation

* freezer: more testing around close/open

* rawdb/freezer: address review concerns

* freezer: fix minor review concerns

* freezer: fix remaining concerns + testcases around truncation

* freezer: docs

* freezer: implement multithreading

* core/rawdb: fix freezer nitpicks + change offsets to uint32

* freezer: preopen files, simplify lock constructs

* freezer: delete files during truncation

This change implements EIP-868. The UDPv4 transport announces support
for the extension in ping/pong and handles enrRequest messages.

There are two uses of the extension: If a remote node announces support
for EIP-868 in their pong, node revalidation pulls the node's record.
The Resolve method requests the record unconditionally.

These changes fix two corner cases related to internal handling of types
in package rlp: The "tail" struct tag can only be applied to the last field.
The check for this was wrong and didn't allow for private fields after the
field with the tag. Unsupported types (e.g. structs containing int) which
implement either the Encoder or Decoder interface but not both 
couldn't be encoded/decoded.

Also fixes #19367

cmd/faucet: remove Google+ mention from web assets too

* core, eth, trie: bloom filter for trie node dedup during fast sync

* eth/downloader, trie: address review comments

* core, ethdb, trie: restart fast-sync bloom construction now and again

* eth/downloader: initialize fast sync bloom on startup

* eth: reenable eth/62 until we properly remove it

* les, light: implement ODR transaction lookup by hash

* les: delete useless file

* internal/ethapi: always use backend to find transaction

* les, eth, internal/ethapi: renamed GetCanonicalTransaction to GetTransaction

* light: add canonical header verification to GetTransaction

p2p/discover: fix nil-dereference due to race

* move error variable to error.go

* Update error.go

Edit "Genesis" to "genesis"

* core: fix import errors on clique crashes + empty blocks

* cosensus/clique, core: add test for the mirrored state issue

* core: address todo question wrt log count

* core: raise a louder warning for non-clique known blocks

swarm v0.4-rc1

swarm/storage: remove traces for put/get/set (#1389)

* swarm/storage: remove traces for put/get/set

* swarm/storage: remove Has traces

swarm/storage/localstore: add gc metrics, disable flaky test

swarm/storage/localstore: fix broken metric (#1373)

p2p/protocols: count different messages (#1374)

cmd/swarm: disable snapshot create test due to constant flakes (#1376)

swarm/network: remove redundant goroutine (#1377)

swarm/network: add want delay timer to syncing (#1367)

swarm/network: synchronise peer.close() (#1369)

swarm/api: integrate tags to count chunks being split and stored
swarm/api/http: integrate tags in middleware for HTTP `POST` calls and assert chunks being calculated and counted correctly
swarm: remove deprecated and unused code, add swarm hash to DoneSplit signature, remove calls to the api client from the http package

* swarm/chunk: add tags backend to chunk package

swarm/network: measure how many chunks a node delivers (#1358)

* swarm/shed: remove metrics fields from DB struct

* swarm/schunk: add String methods to modes

* swarm/storage/localstore: add metrics and traces

* swarm/chunk: unknown modes without spaces in String methods

* swarm/storage/localstore: remove bin number from pull subscription metrics

* swarm/storage/localstore: add resetting time metrics and code improvements

cmd/swarm/swarm-smoke: improve smoke tests (#1337)

swarm/network: remove dead code (#1339)

swarm/network: remove FetchStore and SyncChunkStore in favor of NetStore (#1342)

 cmd/faucet: embed git commit hash/date, disable Google+