* Resolves#1027: Adding interfaces Database, ReadTransaction and Transaction.
* Moving implementations into DatabaseImpl and TransactionImpl.
* Also removed deprecated class Cluster.
As we changed the interfaces, especially how we create transaction, its
going to break the compilation of any app upgrades to this version of
flow bindings. It doesn't change any of the fdb_c APIs. So, backward
compatilbity with old servers is preserved through multi-version client.
* Fixing indentation
* Fixing format according to review comments.
This takes advantage of the new actorcompiler functionality to avoid
having duplicate definitions of `Void _` when trying to feed the
un-actorompiled source through clang.
Alex Miller