Generalized matrix Rayleigh quotient (GMRQ)

I am slowly going to port over the stuff I've been working on, which was in the `commands` branch, into this PR. I just submitted the paper on this stuff "Variational cross-validation of slow dynamical modes in molecular kinetics" for review this afternoon. It is on [arXiv](http://arxiv.org/abs/1407.8083).

- [x] Add MSM score function
- [x] MSM score function tests 
- [x] add tICA score function
- [x] tICA score function tests
- [x] add example notebook