todo:
* finish DBUS stuff:
- - enforce limits
- allow NUL bytes in TXT records
-* release!
* add internal error codes
-* add entry_group::reset()
+* release!
later:
* support for special domain PTR records based on local IP subnet address
* sensible logging
* c++ support
* drop trailing dot on avahi_normalize_name()
+* add entry_group::reset()