Implement public C API and library

[jryans]

It is probably to early to do this because the internals of JFS are still in flux.

However at some point we should implement a public C API and build a library. This library would need statically incorporate the LLVM support library but it should not incorporate libZ3 so that existing users of Z3 can just link against are library too and have a single copy of Z3.

We should hide all the internal symbols of JFS and only expose the C ones so clients don't see the internal details.