Handshake Support

[tynes]

Working on adding a handshake module.

These changes needed to touch the bip32 and core modules as well.

• Input
• Output
• Transaction
• Encoder
• Builder
• Network

Need to revert changes to other modules and address various nits, then this should be good to go

• Port bitcoins: ensure witnesses size matches inputs size #58
• Port core: don't allow syntactically invalid txs to be created #61

[tynes]

Added the covenant field to the output and have some very basic tests. It compiles now, still need to rebase and remove changes to modules other than core.

[tynes]

I think that bitcoins/src/enc/bases.rs should be moved to the coins-core crate. I have an almost copy/paste of it included in this PR.

[prestwich]

unfortunately with the rename a lot of stuff moved around.

I'm fine moving bases to core

[prestwich]

can we do a core fully generic version and then a specialized wrapper in each crate?

[tynes]

I think a thin wrapper over bech32::encode in core that handles common error cases and then wrapping that in each crate with network specifics makes sense.

[tynes]

Build failed for unknown reason 🤔

No output has been received in the last 10m0s, this potentially indicates a stalled build or something
wrong with the build itself. Check the details on how to adjust your build configuration on:
https://docs.travis-ci.com/user/common-build-problems/#build-times-out-because-no-output-was-received
The build has been terminated

[prestwich]

Gonna try restarting it

[prestwich]

Can you add handshake build and test to the ./build.sh script?

[tynes]

Can you add handshake build and test to the ./build.sh script?

#75

Although the build failed again with the same error message