SIPP Tests
* added 01-03

Code
* save totag after call created
* delete_call () clears transaction data
* first_invite handles flow before ringing better
* invite_cb () checks for valid transaction
Documentation
* added README

Testing
* Fixed SIPP files
* added new ones

Code
* adjusted to support changed get_debug_level () API
Test
* renamed FullDialog to PRACK and ACK versions

Code
* test that call-id not exist before creating
* fix locking in create_call ()
* fixed crash on callbacks for bye and refer
* release active transaction in delete_call ()
* PRACK only if required
Testing
* renamed to be more specific
* added cancel scenario
* removed unnecessary comments
* Supported => Require for 100rel

Code
* corrected return values for message processing
* find_call () checks for INVITEs that timed out
* changed wording for missing REFER error message
* added TMCB_DESTROY check if transaction times out
* checks for INVITE cancel
* suppressed compiler warning about nret uninitialized
* changed wording for PRACK ringing message
* checks for PRACK timeout
Code
* cleaned up all error paths (fixed crashes)
* added support for INVITEs that get stuck
* adjusted code to avoid compiler warnings
* PRACK only invoked if Require: 100rel set
* fixed bug that allowed a new call to be created more than once
* adjusted to support changed get_debug_level () API

Tests
* added sipp (http://sipp.sourceforge.net) tests to check code

Documentation
* added README
* updated NOTES