Used a technique similar to lavc/tdsc.c for invoking the MJPEG decoder.

This commit adds support for:
- DNG tiles
- DNG tile huffman lossless JPEG decoding
- DNG 8-bpp ("packed" as dcraw calls it) decoding
- DNG color scaling [1]
  - LinearizationTable tag
  - BlackLevel tag

[1]: As specified in the DNG Specification - Chapter 5
Signed-off-by: Nick Renieris <velocityra@gmail.com>