o For Y'CbCr buffers, changed "unsigned char *" to the even less ambiguous
"uint8_t *", because that is precisely what they are.
o For y4m_read() and y4m_write(), changed "char *" to "void *", which more
accurately reflects their use as wrappers for read() and write().
(Internally, cast to "uint8_t *" in order to do some byte-wise pointer
arithmetic.)
o All other "char *" refer to character strings, and have been left alone.
