F/facility range

This branch implements range support in the facility filter, like that:

facility(local0..local6)

This actually fixes a docbug by implementing it, although only the example uses the previously unsupported syntax, the general description is O.K. Here is the documentation link:

https://www.balabit.com/sites/default/files/documents/syslog-ng-ose-3.3-guides/en/syslog-ng-ose-v3.3-guide-admin-en/html/reference_filters.html#filter-facility