tags2{mwe,sst}.py: refactor so functions are available to convert between data structure formats as well as from TSV strings to data structures
LabeledSentence.__unicode__()
subdivide main() into option parsing, setup, and prediction functions and add a per-sentence analyze() function that returns the output in a dict. This allows the tagger to be imported as a module in other Python code. Fixes #11.
don't report meaningless overall accuracy score