normalize_table

add normalization techniques that have been suggested as alternatives to rarefying.  now using Rscript and with tests.
This should be ``type='choice'``, not ``type='multiple_choice'``, since it's an ``if/elif`` below (i.e., users can't actually pass multiple choices). 

Also, the default doesn't make sense here. It needs to be one of the choices, or be a required option.