Use ? instead of {0,1} and {3} instead of {3,3} where applicable.
Number groups [ß-9] are left as is for readability, i.e. prefer
[1-9][0-9] over [1-9]\d.
The whole expression is evaluated case-insensitive now, so we can omit
the "a-fA-F" and simply use "a-f".
Unit-tests extended accordingly.
The plugins purpose is to exclude or filter certain requests from
tracking by Statify. However the current name "Statify Blacklist" is not
actually inline with today's understanding of such terms. In WordPress
Core 5.5 the word "blacklist" among others has been replaced by more
precise wording where possible.
The term "filter" has been used in various places already and clearly
describes the behavior of this plugin. So we rename the plugin to
"Statify Filter" and rephrase front-end texts.
Plugin slug (permalink), textdomain and all public class and constant
names left untouched for now, to not introduce breaking changes at this
point. To be cleaned up with next major release.
In addition to the pre-existing normal and regular expression filters a
keyword mode is added. This filter matches if the referer string
contains a given keyword (case insensitive).
