Codegen generating deserializers and serializers for the JDWP commands

[wekesa360]

This PR addresses issue #57, creating command classes containing serializer and deserializer functions and grouped into a single file based on a command set.

[michalgr]

I think I would break this task into the following PRs:

1. Generate NewTypes corresponding to values of PrimitiveType enum. It will be a good idea to keep different kinds of ids distinct, pyre will help us not mix things up.
2. Generate dataclasses/NamedTuples corresponding to commands and resonses (only fields for now).
3. Propose input stream and output stream interfaces
4. For each command/response generate parse and serialize methods.