To access this functionality; the -x flag can now be called in the
following ways:
-x file
-x file:<file>
-x author:<author name>
-x email:<email>
Just passing -x file will presume that the filtering rule is intended for
a file (just like the previous behavior).
All the filtering is case sensitive (even filtering by email) in order to
not break any regular expressions used. Case-insensitive matching can
instead be easily achieved with the appropriate regular expression.
To get reversed filtering (excluding everything not matched within -x) a
regular expression with the a syntax such as '^(?!<rule>)' can be used.
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