Generate build info files

Application may access the global char array zrtpBuildInfo to get information
about the ZRTP version, git commit id, and the ABI. The C string contains the
information in three fields, sperataed by a colon in the order depicted above.

This commit also supports Android ndk-build for a armeabi-v7a library.
Merge branch 'v7a' into develop
Merge branch 'develop'
Merge branch 'master' of github.com:wernerd/ZRTPCPP