Prepare V4.2.0
Merge branch 'develop' of github.com:wernerd/ZRTPCPP into develop
Add defines for MS C-compiler
Fix return value of zrtp_getSasType call

The caller now gets a new buffer allocated with malloc(). The caller must
free() the buffer if it does not use it anymore.
Fix replay and ROC computations

The wrong computations lead to false replay indications and to wrong
HMAC, thus they dropped to much packets, in particular under bad network
conditions.
Prepare V4.2.1 release
Merge branch 'develop'