define case and hash equality for etc classes

RGSS also defines #=== and #eql? for Color, Tone, and Rect:

  Color.instance_method(:==) == Color.instance_method(:===)   # => true
  Color.instance_method(:==) == Color.instance_method(:eql?)  # => true
Merge pull request #65 from cremno/define-case-and-hash-equality-for-etc-classes

define case and hash equality for etc classes