Add support of iOS devices (sprite size limitation)

[franciscolourenco]

iOS devices with retina display are limited to 2048px x 2048px images.
If the packed sprite passes these dimensions, the image will not load.

Two things could be done about this:

1. Tuning the packing algorithm to make an effort to create square sprites in order to maximize the space.
2. Split packing in multiple sprites each inside the dimension limit.