Support for Canon Powershot S100 (.CR2)

[arturoisilvia]

I request support for Canon Powershot S100 (.CR2) with the following parameters:
Level 0 -> 128
Level 1 -> 128
Level 2 -> 128
Level 3 -> 128
white point -> 2990

Thank you.

[kmilos]

Just to clarify, this is a request to revert part of #578 for S100 only.

[LebedevRI]

That change is correct, we read reasonable values from the makernotes:

whitePoint: 2976
blackLevelSeparate: (2 x 2) 128 128 128 128

what isn't however correct, is the rest of the hardcoded stuff,
because after sampling the hardcoded black areas we get:

blackLevelSeparate: (2 x 2) 65535 65535 65535 65535

Refs. #389.