Makefile: Use Python2.7's 'unittest discover'

The new-in-2.7 command gives an easy way to run tests that preserves
the usual import mechanism [1].  The old way was giving me a number of
errors like:

  ERROR: test_figshare_add_category (__main__.TestLog)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "figshare.py", line 247, in setUp
      from pyrdm.publisher import Publisher
  ImportError: No module named pyrdm.publisher

Unless I used 'PYTHONPATH=.. python $$file' to invoke the tests.

[1]: https://docs.python.org/2/library/unittest.html#test-discovery
Convert 'print ...' statements to use Python's logging module

The logging module makes it easy to adjust the verbosity, output
location, and formatting of these messages [1].  I've setup the logger
so that users will only see error messages by default, but they can
use --log-level to get more verbosity if they want.  For example:

  $ ./bin/pyrdm-publish --log-level info ...

[1]: https://docs.python.org/2/library/logging.html
Merge pull request #3 from wking/logging

Convert 'print ...' statements to use Python's logging module.

Also use 'unittest discover' in 'make unittest'.

Thanks to @wking for this contribution.