First version of Game module with add_player.  Supervisor now doesn't create tanks but has an API call to do so.
Eliminate tank list, move into a map in Game state.  Document the message handlers that need to get implemented in websocket handler.
Start moving update functionality into Game
mostly done refactor of back-end into multiplayer
added start_link function to game.ex, app launches now
Some cleanup, fix a couple obvious bugs.
Add Amrita and write a couple example facts for tank physics
refactor tank physics test a bit
Players can connect with a name, and multiple players get different player IDs
clean up debugging output, register tank processes by name that interpolates the player id
fix player test
Fix some bugs with Game module. Update loop doesn't crash now.
Clean up front-end interface for better debugging
Merge branch 'master' into multiplayer
re-enable tank update loop