Update libsecp256k1

crypto/secp256k1/libsecp256k1/.gitignore

crypto/secp256k1/libsecp256k1/.travis.yml

crypto/secp256k1/libsecp256k1/COPYING

crypto/secp256k1/libsecp256k1/Makefile.am

crypto/secp256k1/libsecp256k1/README.md

crypto/secp256k1/libsecp256k1/TODO

crypto/secp256k1/libsecp256k1/autogen.sh

crypto/secp256k1/libsecp256k1/configure.ac

crypto/secp256k1/libsecp256k1/include/secp256k1.h

crypto/secp256k1/libsecp256k1/include/secp256k1_ecdh.h

crypto/secp256k1/libsecp256k1/include/secp256k1_recovery.h

crypto/secp256k1/libsecp256k1/include/secp256k1_schnorr.h

crypto/secp256k1/libsecp256k1/libsecp256k1.pc.in

crypto/secp256k1/libsecp256k1/obj/.gitignore

crypto/secp256k1/libsecp256k1/src/basic-config.h

crypto/secp256k1/libsecp256k1/src/bench.h

crypto/secp256k1/libsecp256k1/src/bench_ecdh.c

crypto/secp256k1/libsecp256k1/src/bench_internal.c

crypto/secp256k1/libsecp256k1/src/bench_recover.c

crypto/secp256k1/libsecp256k1/src/bench_schnorr_verify.c