Implement "IPT" colourspace.

Closes #114.
Fixed docstrings.

Aligned first line of reference to next tab.
Instead of repeating the main reference in each function, it is now cited using standard reST citations
Fixed typo in function signature IPT_TO_XYZ -> IPT_to_XYZ
Added module methods to sub-package __init__.py file
Implements unit tests for colour.models.ipt module
Code formatting.
Add missing documentation building dependencies to "setup.py" file.
Add "zenodo" DOI badge.
Change "colour.colorimetry.lightness_1976" definition signature.
Update "colour.colorimetry.lightness" module references.
Update docstrings and inner variable names in "colour.temperature.cct" module.
Update docstrings and inner variable names in "colour.colorimetry.lightness" module.
Update various docstrings in "colour.colorimetry.luminance" module and change "colour.colorimetry.luminance_1976" definition signature.
Update various docstrings in "colour.colorimetry.lightness" module.
Update ".gitignore" file.
Update "Numpy" version in "setup.py" file.
Add disappeared "CIE Illuminant D Series" "D60" chromaticity coordinates for "CIE 1964 10 Degree Standard Observer".

Reference #27.
Remove unneeded commented code.
Add "Sharp" and "CMCCAT2000" chromatic adaptation transforms.

Closes #119.
Update various docstrings.