Forked from https://github.com/apoelstra/rust-secp256k1

The forked repository is tracked into a branch called 'vendor'. The master
branch of this repository contains our modifications on top of that. To
update from upstream:

    git remote add upstream https://github.com/apoelstra/rust-secp256k1
		git checkout vendor
		git pull upstream secp256k1-zkp
		git push origin vendor
		git checkout master
		git merge vendor
		git push