Idea for message serialization

keev - a Key-Value Serialization format with a concept of optionality on each side.

tl;dr:

• All messages exist in a "top level" namespace
• There is no versioning of messages. New message, new number.
• Protocol speakers should expect to "negotiate" which versions they CAN speak, and which they will use.
  • Input/Output capabilities?
  • This should probably only happen once, on connection
• For anachro: Remove the concept of paths
• Use an enum, make it non-exhaustive
• Have a method for generating the RX and TX capabilities