i) implemented issue #1 solution as anrem-target-group* set of functions
ii) added sample demo to show how to use anrem-target-group functions
i) added possibility to get a list of modules that have content subscribed to a group, this can be useful for building the -I switch of a rule that uses the group as dependency
Merge branch 'target-groups' into devel

Conflicts:
	mk/functions.mk