New tags support for writing DNG

[storyboardcreativity]

[Implementations]

• Added enum values: TIFFTAG_BLACK_LEVEL_REPEAT_DIM, TIFFTAG_AS_SHOT_NEUTRAL, TIFFTAG_AS_SHOT_WHITE_XY, TIFFTAG_CALIBRATION_ILLUMINANT1, TIFFTAG_CALIBRATION_ILLUMINANT2
• Added tag BlackLevelRepeatDim (DNGImage::SetBlackLevelRepeatDim)
• Added tag CalibrationIlluminant1 (DNGImage::SetCalibrationIlluminant1)
• Added tag CalibrationIlluminant2 (DNGImage::SetCalibrationIlluminant2)
• Added tag AsShotNeutral (DNGImage::SetAsShotNeutral)
• Added tag AsShotWhiteXY (DNGImage::SetAsShotWhiteXY)

All changes are based on this source: https://graphics.stanford.edu/papers/fcam/html/_t_i_f_f_tags_8cpp_source.html

[syoyo]

@storyboardcreativity Thanks! Merged!