unified api for controllers

[freeman-lab]

In hexaworld-core we need to assume the provided controller will conform to a particular API, which so far means the minimal requirement that it has a keysDown property. Already, this works for crtrdg-keyboard and crtrdg-tty but not crtrdg-touch (due to a naming difference). It'd be really cool to define a common API for controllers, maybe as a test suite, and then here just assume we're using one of them. Can probably move the conversation to one of the controller repos.

cc @sethvincent

[freeman-lab]

One idea, at least for the keysDown / down property: how about replacing it with input, so that way it's touch.input, keyboard.input, and tty.input, all of which seem pretty reasonable?

The events are still different, namely keyDown and keyUp for the keyboard-related ones and tap... and swipe... for touch. But maybe those could be switched to inputOn and inputOff?