Unify Ripser.py and Cechmate interfaces

[sauln]

As an extension of #6, we should also update the interfaces to abide by fit_transform

Currently, the Ripser.py Rips object uses fit_transform to construct the diagrams. Cechmate uses build to construct the filtration and diagrams to build the diagrams.

We should convert cechmate so that fit builds the simplices and transform constructs the diagrams.

[catanzaromj]

Doing this now in #33