Improved packing algorithm

[crobi]

The algorithm (bottom up quad tree packing) is only good if all input textures are power-of-2 squares. Use a general bin packing algorithm, e.g. http://www.csc.liv.ac.uk/~epa/surveyhtml.html

[crobi]

See also http://stackoverflow.com/questions/1213394/algorithm-needed-for-packing-rectangles-in-a-fairly-optimal-way