Add functions to get the ZRTP build info string
Fix handling when parsing ASCII with minus sign
ZRTP can now use Curve3617 if it uses bnlib library
Add Curve25519 Diffie-Hellman key agreement
Change License from GPL to LGPL

In general files that hold my Copright are now using LGPL. Other sources in
this project may have their own licenses. Please refer to the source files.
Prepare a V4.0.0 release
Add handling of auxilliary secret
Enable non-NIST curves for this client's Android
Merge branch 'develop' of github.com:wernerd/ZRTPCPP into develop