Add gratipay shield
Initial version of configurable requireMatchingFilename.
Add some more specs.

Maybe redundant, but just for sanity.
Add option validation
Handle multiple rules in a list
Validate casings and allow dash case.

Map dash to param in `change-case` module.
Update docs for configurable requireMatchingFilename
Update requireMatchingFilename to be configurable.

Closes #5.

Merge branch 'feature/configurable-require-matching-filename'