Merge branch 'develop'
Merge branch 'develop' - rename aes_init to avoid name clashes
NEWS and CMakeLists for V4.2.4
Add functions to read the 'secure since' field from cache
TIVI - change SDES wording to SDP/S
Add functions to set retry counters and cap time

An application may set retry counters and cap time depending on network
conditions. An application must take care regarding if the retries are too big
and if it suppresses RTP during ZRTP negotiation after the "Hello" phase.