Implement and update Cbor encoding

[austinabell]

• Completes Setup and investigate consistent cbor encoding/decoding #35 and refactors previous work done (but keeps the Cbor trait for convenience for encoding structs easier)
  • Note the unmarshall function on the trait was removed, it didn't add much value and required all types which implements the trait specify a lifetime, which gets unnecessarily tedious)
• Change all references for serde related dependencies, only one that still uses serde is needed for the Serialize and Deserialize derive macro (since the macro puts serde as plain text and can't alias)
• Sets up IPLD visitor to decode cbor encoded bytes as IPLD (step toward or might be replaced with Review Readiness of Rust IPLD libraries for IPLD Store #111 depending on libraries usage)
• Changes gas_price and gas_limit to u128 from BigUInt because deriving serialize on that type is a huge mess, but will either create a type for the gas values, or wrap the big ints to more easily define the serialization functions on them and make it more usable (Wrapper for BigInt type #130 BigInt wrapper and local types #135)

Will open this up as draft until I write tests for all of this. I can either open this now and add extensive tests in another PR or just add them and open after. Would love input either way to see what you guys think of this direction (specifically the Cbor trait we have)

[ec2]

Big chungus PR... Absolute unit

[dutterbutter]

Great work on this @austinabell 🔥🔥🔥🔥

[ansermino]

This is missing a lot of docs