Update README.md

Add TravisCI build icon.
Fix code issue
Refactoring event names, internal namings.
Externalize event hooks internally.
Oops.. introduced a bug: Fixate the meaning of the variable correctly.
Extend method api design using socket directly as an argument.
Remove logging
Improve demo-script.js to control the player's step & result.
Add helper to find playerType by socketId.
Simplify de-register of a client.
Fix typo.
Add move (public move) and preMove (in player group move).