Issue 372 up to datasets

Addresses #372.

This pull requests concerns the documentation in pylearn2/doc (api_change, cluster, ..., overview, vision), pylearn2/doc/internal, and pylearn2/doc/library from "alex" to "datasets"

@dwf, do I have to modify the formatting of the parameters in pylearn2/datasets/retina (i.e. remove bullet points and write parameter types explicitely)?