Spec for StarkNet

[delaaxe]

Adds CAIPs for StarkNet.

[bumblefudge]

Hey @delaaxe :

I think it would help to add a starknet/readme.md file that does a little ELI5 on all of the bare-minimum Cairo-specific assumptions which would be footguns for, say, a completely uninitiated Solidity or Solana dev. In many namespaces, I simply write that readme.md myself on the back of a few hours of reading around in Improvement Proposals and VM core docs, but I have to confess I could not exactly define what a felt is in "just tell me the bare minimum I need to know" terms, even after reading all the following carefully and repeatedly:

• https://starknet.io/docs/reference/syntax.html#type-system
• https://starknet.io/docs/how_cairo_works/cairo_intro.html#field-elements
• https://medium.com/nethermind-eth/field-elements-all-the-way-down-59f02387d1d6
  I am vaguely grokking how the == operation declares a field element by checking it and what write-once means, and why a struct is needed for EVM transpilation, but I would not feel confident "supporting" the network passively or querying it without submitting transactions. Perhaps linking to resources specifically focused on cross-VM development would help?

Think of it this way-- dapp and wallet devs need to be able to implement a namespace without necessarily learning Cairo well enough to read, much less write, a real-world Cairo contract. They need the assumptions and risks of addressing a contract, asset, or entity on starknet spelled out for them, which is what the ideal namespace does.

[bumblefudge]

More generally, you might think of CAIP10s and CAIP19s as "export formats" for addresses and assets in the system-- if there is a standardized and deterministic way to represent modulo-P/felt addresses and assets in modulo-2^256/"EVM-mode", that might be preferable to a lossful or arbitrary transformation of canonic representations

[delaaxe]

@bumblefudge I added a readme