Add console library.

The console has five methods(log, info, warn, debug and error).
Those method have to be implemented with variable length argument but
rhino cannot passes variable length argument to Scala native object,
because Scala implements variable length argument with Seq but rhino
doesn't know about Seq. So console passes one string converted with
JavaScript.
Add util.event API.

This API is for logging game event with JavaScript.
The first argument is tag, and others are messages.

The messages are logged in the one of the three form.
 - Object -> message itself.
 - Only one message -> { "message": message }
 - Multiple messages -> { "message": [ message1, message2, ... ] }