Improve filter support

[jtojnar]

The filter expression can take one of the following forms:

1. An atomic filter: a Perl-compatible regular expression, as accepted by PHP, between forward slashes (/). For example, /reg(ular expression|ex)/ will keep only items whose title or content matches the regular expression between the slashes (i.e. contain the phrase “regular expression” or “regex”). Learn more about regular expressions on https://www.regular-expressions.info/.
2. A field-specific filter: an atomic filter preceded by one of the field names below and a colon:
   • title:/regex/ will keep only items whose title matches the regular expression between the slashes.
   • content:/regex/ will keep only items whose content matches the regular expression between the slashes.
   • author:/regex/ will keep only items which have an author that matches the regular expression between the slashes.
   • category:/regex/ will keep only items which have a category that matches the regular expression between the slashes.
3. A negated filter is either an atomic filter or a field-specific filter preceded by an exclamation mark (!). It will only keep items would not be kept by the filter after the exclamation mark.

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[GutHib]

Wow, that is truely amazing. Does the project accept donations or should that go towards a charity?

[jtojnar]

I can send you an IBAN number if you want to do a bank account transfer. But donating to Internet Archive or Wikimedia Foundation is also fine.

[GutHib]

Mail sent to your gmail address, you can find it in your spam folder.

[jtojnar]

@GutHib Thank you for your donation :heart: