Added ociobuildicc app which will build a soft-proofing icc profile for a given working space.
(added LCMS2 into ext)

Commits:
https://github.com/malcolmhumphreys/OpenColorIO/commit/1b0d39fb10db10f4edbf1fb0fed124b548b836d9

Attached is an example of two profiles in action.

From the left
* sRGB reference image (ocio cpu)
* matte paint allocation space
* log space image.

The visual difference in the log image is most likely caused by 16bit quantization errors in the
CLUT of the AToB0Tag. These errors are less with the matte paint allocation as the distance
to travel is less.

I did play around with supporting the new MPE D2Bx and B2Dx tags which should make this
problem go away (http://www.color.org/ICCSpecRevision_02_11_06_Float.pdf) but couldn't
get it too work reliably so I pulled it out till I can.

.malcolm