Adapted Tom Barron's config file contribution.
It still needs to be tied into actual cmdline processing.
- Updated CHANGELOG
- Refactored the (excellent!) test cases to account for the changes I
  made.  Removed the duplicate documentation and unused code.
- Refactored the config loading: 1) Removed the caching 2) Took
  advantage of ConfigParser's native ability to merge multiple config
files.
- Removed trailing whitespace, renamed a few things to be more readable,
  re-spaced between functions and classes (because I like lots of
vertical whitespace)
- Added module documentation to the config module
- Improved the "--config" option description and metavar.
- Moved the config module loading in cmdline until after coverage is
  initialized
- Removed the cmdline module debugging, including the "--cmdcheck"
  debugging option.
- Added debug output to the config loading.