Adding local path if none specified

This was one of the first tools I installed on my Mac in preparation for VIM
hacking just to discover it does not work for BSD-based ``find``.  The issue is
``find`` needs to have a path specified.

This pull is an attempt to add the local (".") path if a path is not specified.
I moved ``README.txt`` to ``README.rst`` and added some more notes.  I also
updated the unit tests.  I can split up these commits if they are not necessary.

I also completely understand if this is an unnecessary pull request!

As a side note I'm still working on detecting ``xargs`` features as
``--no-run-if-empty`` is not a valid option for Mac ``find``.