Comparison should be case in-sensitive

[bbuehrle]

All words to be filtered should be lower-case, regardless of how entered. Word to be compared should be lower-case, regardless of how entered.

[bbuehrle]

I completely wing-ed this. I'm not sure yet how to add any test to check if this works, but point me in the right direction and I can try to add that as well.

[hanzei]

Looks good to me 👍

Unfortunately there aren't any tests yet, so it's fine to merge is as it is.

[iomodo]

Thanks @bbuehrle ! LGTM!