Use QChar::isSpace instead of a list of spacing characters
Allow regular expressions in patterns matching literal values
Add passes to split units from integers and to recognize file sizes

This greatly simplifies the Numbers pass, that does not have to bother
with file sizes.
Run the parsing passes in a loop, as each pass can expose further refinements
Detect comparison operators followed by values
Simplify the pattern language

Translators do not need to know that the parser wants to match a comparison
operator, a literal string or a type hint. This kind of matching is now done
directly into the passes.
Match arbitrary properties using langage-dependent rules

Now the parser does not only match "sent by X", but also a small set of
properties related to emails and files.