Add BaseEncoding to replace encode_b58, decode_b58, encode_multibase, decode_multibase

[cycraig]

Description of change

Replaces the encode_* and decode_* utility functions with a new BaseEncoding interface with static methods. This allows us to remove several dependencies for bs58 and hex encodings.

Note: this does not affect the Wasm bindings, since we did not export the base encoding utility functions anyway, should we?

Added

• Add BaseEncoding.
• Add BaseEncoding::encode.
• Add BaseEncoding::decode.
• Add BaseEncoding::encode_base58.
• Add BaseEncoding::decode_base58.
• Add BaseEncoding::encode_multibase.
• Add BaseEncoding::decode_multibase.

Removed

• Remove encode_b58.
• Remove decode_b58.
• Remove encode_multibase.
• Remove decode_multibase.

Type of change

• Bug fix (a non-breaking change which fixes an issue)
• Enhancement (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Fix

How the change has been tested

Added unit tests, existing tests all pass.

Change checklist

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[olivereanderson]

Looks good to me.

Thanks for the improved docs and additional Base58 tests.