o Actually commit the *code* for the y4m_chroma_ss_[xy]_ratio() functions.
o Smack myself in forehead twice (for good measure).
Note to those who read notes:
y4m_chroma_ss_[xy]_ratio() returns the scaling ratio "n:d" by which the
chroma planes are subsampled/scaled from full resolution. This means,
more or less, that any regions defined on a frame need to be aligned to
a multiple of "d" pixels --- since to a zeroth-order approximation, "d"
luma pixels correspond to "n" chroma pixels.
-matto
