Add programmtic interface

I found myself really wanting a programmatic interface to check strings without having to write to files. This is a simple function for doing so.
Spencer, I'm just about ready to merge this.  I just found this minor issue in that this filelike is no longer getting closed.  I wouldn't have noticed it at all except running the unit tests on python3 printed out:

pgsanity/test/test_pgsanity.py:41: ResourceWarning: unclosed file <_io.TextIOWrapper name='/tmp/mdrago/tmpls__2f_u.pgc' mode='r' encoding='UTF-8'>

Running the tests on python2 did not produce the same warning - I'm chalking that up to improvements in the unittest module.  Once you make that change I'll merge this, increase the version, and push it out.  Thanks again!