Ignore case when matching

[dechamps]

Currently, it looks like https://rssfilter.netlify.app/ will match regexes in a case-sensitive way.

This is unlikely to be what the user wants - if I set up a title match for "animal", I'd be surprised by "Animal welfare" not matching purely because the A is capitalized.

It would make sense to switch the default to be case-insentive, or at least provide it as an option.