Rank submodule

[CCampJr]

Submodule to estimate rank of the data.

Methods to incorporate (so far):

• SVD/PCA + various metrics (I do a lot of these)
• HySime
• SIMPLISMA (@ClarkAH)
• IND and RSD (@sshojiro )

Implementation considerations

• Out-of-core analysis
• Python vs Cython for some
• ?

Note that rank approximation is not a trivial task. It's super-easy to get an estimate and seemingly easier to be incorrect. Kind of the reason I didn't incorporate this feature into the 0.3.0 release.

My plan is to create a super class RankEst that all subclasses will inherit. This class will likely incorporate some metrics to describe confidence or error -- not sure.

Questions and comment welcome!