Added CCFLAGS to compile

This changes allows to compile raspi_dng with debug-information, e.g.
  make CCFLAGS="-g"
Extract red and blue gains and pass to raspi_dng
Read additional argument containing the pair red_gain,blue_gain

The gains are written directly into TIFFTAG_ASSHOTNEUTRAL. Green remains 1.
Transition from a simple wrapper to a usefule script

The script now takes a number of options, e.g. to convert with/without
embedded color matrix and wb-gains, or to convert directly to tif using dcraw.
Link with libexif

Added option to link with libexif. Also added patch from master to fix
compilation issue on RPI.
Read color-matrix from EXIF-data

If no matrix is passed in, read the matrix from the EXIF-data (if available).
Removed reading and processing of gains
Support old raw images

Reads model name and uses old cfa-pattern if modelname is "ov5647"
Changed interface to match raspi_dng

Since raspi_dng now takes care of the embedded color matrix, the matrix
option has changed from
  -m        (use embedded matrix)
to
  -M matrix (use the given matrix instead of the embedded matrix)
Raspi_dng no longer takes a fourth argument (gains), therefore raspi_dng.sh
now passes gains only to dcraw.
Updated for version 2.2