Allow passing in full Frame options

[kettek]

This should probably be defined by passing a JSON file, either through STDIN or in the place of the [frame.png ...] arguments. It'd be a simple structure such as :

[
  {
    "image": "...",
    "default": true, // if only first frame
    "x": 0, // xoffset
    "y": 0, // yoffset
    "numerator": 0,
    "denominator": 0,
    "dispose": <strings>,
    "blend": <strings>,
  },
  ...
]