Support for custom presence message body with existing PJSUA-LIB buddy management

[bennylp]

PJSUA-LIB presence management simplifies SUBSCRIBE/NOTIFY mechanism a lot such that there have been some requests to enable application to use custom presence message body (i.e. not PIDF) using the framework.

The new on_buddy_evsub_state() callback has enabled application to process the custom body in incoming NOTIFY requests. Similar feature to allow application to put custom body in outgoing NOTIFY and PUBLISH requests would be required, as well as the ability to specify other event properties such as package name and Accept list.

Thanks Johan Lantz for the suggestion.