Set all regexes to be case-insensitive by default.

It seems like an unlikely use case that anyone would want to differentiate mappings by capitalization. This removes the need for match patterns like `[Ss]print`, allowing `sprint` to match `Sprint`, `sprint` or even `SPRINT`.
Merge pull request #2 from pdclark/patch-1

Set all regexes to be case-insensitive by default.