Clean up and add datasets, improve descriptive functions. Fixes #6, fixes #13, fixes #15.

Enacts most suggestions that have been made regarding the package:

Add datasets that had been added to Vincent's repo.
Remove rownames unless they add information.
Colnames are cleaned in R so that doesn't have to happen on read.
Combat over-factorization of strings, underuse of integers in R.
Save data with ('valid') factors as .rda when possible.
Remove all attributes that break read_rda (functions, formulas, NULL).