Implementde color appearance models, tests and documentation

Notable new additions:
* Added `color_appearance_models` module including the following models: `Nayatani95`, `Hunt`, `RLAB`,   `ATD95`, `LLAB`, `CIECAM02` and `CIECAM02-m1` 
* New section in the documentation giving a short introduction to color appearance models and describing the input parameters, the results and references for each model
* Short example of how to use `CIECAM02` in `examples/color_appearance_models.py`

Small but potentially important things:
* I activated the `sphinx.ext.mathjax` add-on so I could use mathematical notation in the docs.
* I added some legal mumbo jumbo to the new files. Same license as for the overall project, but attributed to me and my university.

A few words about testing:
* the models are verified using independent calculations that can be found here: http://rit-mcsl.org/fairchild/CAM.html (under "Example Calculations and Functions") but not all corner cases might be covered (especially more advanced features of the Hunt model).
* notable exception: `CIECAM02-m1` is currently untested, as no independent data set exists (to my knowledge).

Any feedback is welcome. I am sure there are still plenty of things to do, but things are in a pretty good shape now so they can be reviewed for inclusion.