thirdparty libs strategy and support

I'm trying to port [rust-base58](https://github.com/nham/rust-base58) library. I see that you've ported quite a few libs in third_party but I don't see how these will be supported and updated in the long run. Wouldn't it be better to fork these libs separately and reference them by git path in Cargo.toml?

Is there a recipie about what to do to port a lib?

Review the existing third_party libraries and the rust-base58 port referenced in the issue, then inspect how Cargo.toml currently references dependencies. Determine whether the project has a documented support and update strategy, and identify what a porting recipe would need to cover. Done means the strategy and porting guidance are written down and address the questions raised here.

Written by the indexing model from the issue text.