Fixed bad month index in mailing list reporter.

Fixes #447. Month index check was 12 but should have been 11, so it started breaking in December.
Merge pull request #23 from rhyolight/fix-ml-reporter

Fixed bad month index in mailing list reporter.
Expanding dynamic module loading with exclusions.

Added general utility tests. Tested that all files within a directory are included as modules. Tested that specifically excluded files are ignored.
Reading validator exclusions from config.

And respecting them when creating the github hook handler.
Adding new test for sterilized config.

Because I have to to pass the coverage comparison tripwire I set up.
Merge pull request #24 from rhyolight/configurable-validators

Configurable validators