Binding of libsecp256k1 of Bitcoin ABC implementation

Prerequirement

Environment variable

You can customize build step using following environment variables. - BITCOINABCREPOURL
default: https://github.com/Bitcoin-ABC/bitcoin-abc/tags/v0.19.6/
Repository of Bitcoin ABC.
libsecp256k1 sources are downloaded from ${BITCOIN
ABCREPOURL}src/secp256k1 .