Include support for ZEC and its forks

[Mikerah]

Although ZEC is a fork of bitcoin, adding support for it is partially covered by #3. But, there is no straightforward way to support shielded ZEC transactions in Golang. I'm currently in talks with the maintainer of a ZEC fork called Hush and will be working with him on getting Hush supported in Meson. Hush is a fully shielded fork of ZEC that supports sapling transactions. This will enable us to test out the privacy guarantees of using a privacy coin with a mixnet and can help when applying for Zcash Foundation funding.