Mixins

[giladgray]

Refactor engine to use a mixin architecture that separates concerns.

A mixin is a module that exports an object to merge into pocket.

pocket.use require('./key.coffee')
pocket.use require('./component.coffee')
pocket.use require('./system.coffee')

pocket.use require('./inputs/mouse.coffee')
pocket.use require('./inputs/keyboard.coffee')

# key.coffee
module.exports = 
  key: (components) ->
  keys: (keys...) ->
  getKeys: ->
  destroyKey: (id) ->
  ...