Adds the initial finito-postgres crate with type definitions for the
tables and initial functions to interact with persisted FSMs.
This is far from feature complete at this commit.
Checks in my classic, lockable door example implemented in Finito.
This does not yet contain the documentation of the door in the Haskell
version of Finito.
The implementation of this library is closely modeled after the core
abstraction in the Haskell library. This does not at all concern
itself with persistence, interpretation of effects and so on.
