use LibRaw 0.16.0

LibRaw >= 1.15.0 no longer allows document_mode for grayscale
uninterpolated data, hence now directly reading raw data buffer.

QUESTIONS:
- does this produce different data than document_mode did?
- do need to set so many params for LibRaw if not calling
  libraw_dcraw_process() and libraw_dcraw_make_mem_image()?
basic downsampling for x-trans images
linear demosaic for x-trans files
temperature and highlights modules for x-trans
first pass at hotpixels module for xtrans

there seem to be a lot of hot pixels in shadow areas -- need to
investigate further
first pass at raw denoise for x-trans

looks pretty rough around edges especially
invert module for x-trans
disable ca correct module for x-trans