Merge branch 'Gustav-Simonsson-update_bitcoin_secp256k1_lib2' into develop

crypto/secp256k1/secp256.go

crypto/secp256k1/secp256k1/.travis.yml

crypto/secp256k1/secp256k1/Makefile

crypto/secp256k1/secp256k1/Makefile.am

crypto/secp256k1/secp256k1/README.md

crypto/secp256k1/secp256k1/autogen.sh

crypto/secp256k1/secp256k1/build-aux/m4/bitcoin_secp.m4

crypto/secp256k1/secp256k1/config.mk

crypto/secp256k1/secp256k1/configure

crypto/secp256k1/secp256k1/configure.ac

crypto/secp256k1/secp256k1/include/secp256k1.h

crypto/secp256k1/secp256k1/libsecp256k1.pc.in

crypto/secp256k1/secp256k1/obj/.gitignore

crypto/secp256k1/secp256k1/src/bench.c

crypto/secp256k1/secp256k1/src/bench.h

crypto/secp256k1/secp256k1/src/bench_internal.c

crypto/secp256k1/secp256k1/src/bench_recover.c

crypto/secp256k1/secp256k1/src/bench_sign.c

crypto/secp256k1/secp256k1/src/bench_verify.c

crypto/secp256k1/secp256k1/src/ecdsa.h