Implement ZRTP protocol version negotiation

This version implements protocol negotiation according to RFC6189, section
4.1.1. This new function required modifications on the external interface to
provide additional information from and to applications. See documentation.

Currently the library supports only version 1.1 and is compatible with
previous versions on protocol level.

Applications shall use the new library even if the don't use the new or
modified interface functions. This will guarantee that the application are
prepared once a new ZRTP protocol version is available. Application shall use
the new/modified interfaces if they require and handle ZRTP hello hashes.
Avoid Error packet injection attack
Add SAS type B256
Implement public key algorithm selection according to RFC