func_hangupcause.c: Add access to Reason headers via HANGUPCAUSE()

func_hangupcause.c: Add access to Reason headers via HANGUPCAUSE()

As soon as SIP call may end with several Reason headers, we
want to make all of them available through the HAGUPCAUSE() function.
This implementation uses the same ao2 hash for cause codes storage
and adds a flag to make difference between last processed sip
message and content of reason headers.

UserNote: Added a new option to HANGUPCAUSE to access additional
information about hangup reason. Reason headers from pjsip
could be read using 'tech_extended' cause type.