Progress towards effectively wrapping eunit.

With Robert's fixes to pulling in Erlang macros, lfeunit can return to its
original vision of being a Lisp-y wrapper for eunit rather than a
re-implementation.
Updated README.
Updated ignores.
Fixed up makefile to only download expm when it's needed.
Converted wrapper functions to macros.

And moved them into an include.
Fixed unit tests; re-enabled all.
Fixed to use eunit macro data.
Updated with new test output.
Updated with note about legacy support.
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.