Principally, this adds producing libmentat_ffi.a for consumption by Carthage.
To achieve this, we disable bitcode and bump the miniumum iOS version
to 11. In addition, we make things open and public so that consumers
can, well, consume.
Documents the FFI layer for Mentat, and provides transaction functionality via an EDN string. Creates two native libraries for iOS (Swift) and Android (Java) and fully tests the FFI for both platforms.
Closes#619#614#611