Remove crop/padd code from imgresample module. Imgresample is now only

1 submodule (well, 1 main module) which can take care of resizing and
chroma conversion (basically it's the old chroma.c code). All the files
have been merged in imgresample.c. In the long run I might split
resizing and chroma conversion to 2 submodules (performance impact would
be nil). (This is untested.)