JSON-RPC write extension

[Mirko-von-Leipzig]

Support sending StarkNet transactions via the JSON-RPC API. This enables node service providers to use a single endpoint (pathfinder) to provide full access to StarkNet. Our implementation should simply pass these requests straight through to the sequencer.

Steps

• add support in sequencer client
• add support in JSON-RPC server (this is blocked by having a spec to implement against, but we can start taking an educated guess so long)

Required functions

• deploy: deploys a starknet contract
• invoke: invokes a starknet contract's function
• declare: declares a StarkNet contract class (only available from StarkNet 0.9)

Additional info

The sequencer expects compressed data for a deployed contract's bytecode. We can expect that the caller will do this compression; but it's probably a good idea to document this explicitly in the JSON-RPC spec.

[kkovaacs]

#318 adds support for the missing declare functionality.