Lots of experimenting with deftest macros.

It looks like the 4th one was a charm. Making this commit before I clean it up,
so there's a reference to the process of discovery (macro trial and error...).
Removed unsuccessful macros.

Renamed surviving macro to deftest and updated the unit tests that use it.
Finished converting to deftest.
Finished converting to deftest.
Updated docstrings.
Updated README with latest changes to library.