unlock upscale filters
convert tabs to spaces
Add tests. Rise for "P" and "1".
Add new fast ImagingTranspose function
Hide stretch implementation detail in Antialias.c
two ImagingStretchHorizaontal pass with two transposes
Precompute coefficients for all x
Iterate pixels in native order
move ww into coefficients
make x indexes int
faster float to 8bit convertion