V0.4.1 release

Here's what I have so far. Mostly updated `CHANGES.txt` and did some more PEP8ing.

I updated our Trove (`setup.py`) development status to `Production/Stable`, which we probably should have done a year or two ago. I figure we should save `Mature` for whenever 1.0 happens. :)

I wanted to do a compare of v0.4.0 to this branch on GitHub, but the GitHub web interface chokes on the large number of commits. Please take a look in git? (`git diff v0.4.0 davidmarin/v0.4.1-release`)

Oh, and I decided at the last minute to rename the `check_hadoop_input_paths` option to simply `check_input_paths`, and made the switches more consistent. Would feel better if this had an automated test.

I have *not* yet updated `whats-new.rst`.