Pysigma-backend-uberagent

- Remove rules that are causing false positives.

- Remove rules that are causing many false positives.

pySigma-backend-uberAgent

Changelog
Disable istartswith, iendswith, icontains
Use regular `like` expressions again because of a performance regression.

pySigma-backend-uberAgent

- Fixup handling regular expression escaping.

pySigma-backend-uberAgent

- `isnull` expression not emitted for older versions anymore.

pySigma-backend-uberAgent

- Initial release.