Add a format specification in global tags files and implement an additional fallback if the specification is missing.
Adjust code and scripts which generate global tags files to add the new format specification.
Update global tags files.
Add documentation for the two supported global tags files formats.

git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@3465 ea778897-0a13-0410-b9d1-a72fbfd435f5