Add "Travis-CI" notifications to "Slack".
Implement "__pow__" magic method for "colour.SpectralPowerDistribution" class.
Implement "__pow__" magic method for "colour.TriSpectralPowerDistribution" class.
Fix doctests for "colour.SpectralPowerDistribution" and "colour.TriSpectralPowerDistribution" classes.
Ensure proper "colour.SpectralPowerDistribution.__pow__" and "colour.TriSpectralPowerDistribution.__pow__" methods doctests ellipsis.
Add various new light sources.

Closes #141.
Update various docstrings.
Convert "colour.TCS_SPDS" type to "CaseInsensitiveMapping".
Rename "colour.quality.cri.TSC_COLORIMETRY_DATA_NXYZUVUVW" named tuple to "TcsColorimetryData".
Fix issue in "colour.LIGHT_SOURCES_RELATIVE_SPDS" attribute data.