Numbers and strings sort with as_path.

To do this, numbers had to be wrapped in an extra tuple from natsort_key
when called with as_path, so that there was the same level of tuples
for both strings and numbers.
Added the --paths option to the CL tool.

This option will trigger the as_path option to natsorted. This will
make the natsort command line tool much more useful, since sorting file
paths is likely a common task for natsort.
Added a stress tester.

This stress tester generates random strings and tries to sort them.
Package now passes pyflakes tests.

This was mostly import problems. The setup.cfg has been updated with
options to refine what is checked.
Package now passes pep8 tests.

Some the test_natsort.py script has some line length rules ignored, but
otherwise all rules are obeyed.
'python setup.py test' now does coverage and analysis.

This was done by adding --cov, --flakes, and --pep8 to the pytest call
within setup.py.
Added expanded documentation.

This documentation is in reST format, in a docs folder.  The README has
been pruned to only include what is needed to notify the user of what
the package does, and directs them to the documentation.

The tests and .travis.yml have been updated to account for the
documentation.