add preliminary test suite

[deanmalmgren]

[adding this from memory of some things we discussed doing]

@freemarmoset had some ideas about this as I recall.

[deanmalmgren]

Now that we're talking about including optional settings, here are a couple of tests that come to mind:

1. Make sure the mandatory arguments of selector and data are actually specified!
2. Make sure that catcorr fails gracefully with a useful error message if someone misspells a selector string or passes an incorrect object.
3. Make sure the data is in the correct format and fail gracefully with a useful error message if something isn't properly formatted.
4. If we end up incorporating the options suggested in configurable label settings #29 and configure width/height settings #30, it would also be good to provide useful error messages if options aren't properly specified or if unsupported options are specified (and obviously not doing anything).