UAC functions for event support
UAS first work
Massive dialog update

- Split INVITE and subscription data in dialogs
- Event header added to #sipmsg{}
- Updated callback timer
- Tests passing
Basic UAC and UAS code
Prepare events in #call{}
New dialog code rewrite

Trying a different approach to include event state
Merge branch 'events'
Merge branch 'refs/heads/master' into events
UAC and UAS mostly done
SUBSCRIBE mostly working
Fixed bug in dialog
Tests fixed
Merge branch 'refs/heads/master' into events
First NOTIFY version
Starting tests
SUBSCRIBE/NOTIFY working!

Pending:
* More tests about NOTIFY coming before SUBSCRIBE response and refreshes
* Test interoperability with softphones
* Implementation of a sample event-package (MWI?)
Doc updates