Added subseq and ~subseq operators which match subsequences of strings.
This is useful to filter out matches quicker:
$ ktraderclient5 --constraint "'libremath' ~subseq Name" --servicetype 'Application' --short servicetype is : Application constraint is : 'libremath' ~subseq Name got 1 offers. /nix/store/zq1kgdxk426qgf06nzpd7xqkpk4z5hh2-system-path/share/applications/math.desktop