Fix precision loss due to matrices rounding in "IPT" colourspace model.

References #127.
Removed rounding of LLAB_XYZ_TO_RGB_MATRIX (issue #127).

Tests where updated to use rounded version for testing against the reference data.
Added test to check for precision loss for multiple conversions.
Introduces dependency for mock, when testing with python version lower than 3.3
Added mock to .travis.yml
Updated doctest.
Code formatting.
Merge pull request #160 from colour-science/feature/matrices_rounding

PR: Precision loss due to matrix rounding preventing round trip transformation in "IPT" colourspace model.