Store PubSub item creation/modification timestamps as integers instead
of "$megasec:$sec:$microsec" strings. This can improve the performance
of certain SQL queries significantly.
Thanks to Ammonit Measurement GmbH for sponsoring this work.
Note that support for older specification is completely dropped,
i.e. no backward compatibility is provided since the XEPs are
still very experimental and being changed drastically
Accordingly, Mnesia/SQL/Riak table 'carboncopy' is not used anymore
and can be safely removed.
As a consequence, the commit deprecates the following options of
mod_carboncopy:
- ram_db_type
- use_cache
- cache_size
- cache_missed
- cache_life_time
Fixes#2663