Provide MessagePack serialization

[uint]

This PR does two things:

• modify cosmwasm_core::{Binary, HexBinary} to (de)serialize directly as binary blobs when used together with a compact encoding (meaning one that returns false from is_human_readable), and
• provides a set of new MessagePack-related functions that mirror the JSON API: cosmwasm_std::{from_msgpack, to_msgpack_vec, to_msgpack_binary}.

Breakage

If we're being rigorous, I think the changes to cosmwasm_core::{Binary, HexBinary} are breaking if used for storage with a binary encoding. Maybe we should release this with a major version bump or deprecate these types in favor of some new ones. @webmaster128 you're the decision-maker here.

This is breaking if we assume someone out there has used the binary/checksum types with binary encodings.

We're not bumping the major version for this since as far as we're concerned, that use case has always been unsupported. Still, we're going to release this with a minor version bump, and before it's released we're going to provide some "guard rails" via #2125, #2126, #2127.

TODO

• changelog