Add reStructuredText scope information for tags (for symbol list
grouping).
Read custom system global tags files from $prefix/share/geany/tags;
Closes #2778923.
Show the number of tags in a user global tags file (instead of the
running total) in the debug message.
Also print debug messages when loading a tag file manually or for
default global tags files e.g. python.tags.
- code:
Move NestingLevel tags code into a separate file, add functions.
- docs:
Add 'Installation prefix' section instead of quoting '/usr/local'
each time.
Update for custom system global tags files.



git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@3788 ea778897-0a13-0410-b9d1-a72fbfd435f5