matyalatte

I got two warnings when importing dds in GIMP.  It uses DDSD_PITCH when it should use DDSD_LINEARSIZE. And it uses DDSD_LINEARSIZE when it should use DDSD_PITCH. dds.py says ```python...

Related to #25. Swizzled textures have padding when their texture sizes are not multiples of the swizzling block size. So, UE4-DDS-Tools need a new function to calculate their buffer sizes,...