Raw input: Added new input format for camera raw formats. Uses LibRaw.

Hi,

I've been working on this for a few days, and just wanted to get some feedback. 
Raw format reader powered by LibRaw. Handles most RAW formats.
I've given some attributes to control the most common settings (Exposure, ColorSpace primaries, Demosaic algorithm).
Only thing missing at the moment is the EXIF metadata, but It shouldn't be too difficult to add that in.

Thanks,
Mark