[rsyslog] rsyslog doc licenses

[Rainer Gerhards]

Hi all,

Michael Biebl made me aware that the doc files have inconsistent license
information (thanks!). Some state GPL, some FDL, some even nothing.

I would like to unify them to use GPLv3, which is consistent with the
rest of this project. Does anybody object this move? If so what are the
reasons and alternatives?

Feedback is appreciated.

Many thanks,
Rainer