Packr2

Implements some relevant of packing algorithms, currently StripPacker (simplest), SkylinePacker (good for unsorted data) and SplitPacker (best for bake data using the pack function)

• It uses almost the same interface as texture_packer.
• The SplitPacker was ported from rectpack2D but it sorts all split globably

Work left

• Implement pack_with_best_size function to find the best packing with the lower used area