[Users] RR module changes

[Bogdan-Andrei Iancu]

Hi everybody,

I made some updates to the RR module on both users and developer sides:
    for users: new is_direction() function; more docs about dialog 
support via RR module
    for developers: RR API added; RR callbacks added; docs describing 
both of these (with some examples).

For more and more info, please refer to the online doc:
    http://www.openser.org/docs/modules/0.10.x/rr.html

The RR API and callbacks are not 100% tested, it's on the way - they 
will be used by the UAC module (for FROM/TO mangling) and by other 
future module which will need dialog support.

regards,
Bogdan