users can use say when it's not their turn
Added send-message to send messages to the user

A nicer abstraction than dealing with the mutex and ports directly. broadcast
and say have been reworked to use send-message instead.
Updated engine-test for new state struct
Implemented thief

Seems to work, but not fully tested. In particular, need to test with 3 users
to make sure things like choosing a target work properly.
Finished server-side implementation of thief

Next, need to make the client capable of handling prompts, etc
Added client support for thief/prompts
Minor server message clarification