Move configargparse.py to root of project

- tests/test_configargparse.py: changed configargparse import to match
  new file location
- .gitignore: add the htmlcov directory
- setup.py: remove packages, packages_dir, install_requires from
  setup(), replace with py_modules
- configargparse.py: move to project root and update __version__

There were extra spaces on blank lines and at the end of some lines that
my editor automatically removed. These extra spaces would generate pep8
violations, but are otherwise innocuous.