in progress new API
separate filter for horizontal and vertical
Merge branch 'resample2' into resample

Conflicts:
	stb_image_resize.h
in-progress refactoring
new API "finished" but untested
new API partially in-use
tweak new API, get it partly working
STBIR_EDGE_ZERO
finish STBI_EDGE_ZERO, untested
tweak new API
rename alpha gamma flag