feat(postgres): Bootstrap Postgres persistence implementation

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.

finito-postgres/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "finito-postgres"
+version = "0.1.0"
+authors = ["Vincent Ambo <vincent@aprila.no>"]
+
+[dependencies]
+chrono = "0.4"
+serde = "1.0"
+serde_json = "1.0"
+postgres-derive = "0.3"
+
+[dependencies.postgres]
+version = "0.15"
+features = [ "with-uuid", "with-chrono", "with-serde_json" ]
+
+[dependencies.uuid]
+version = "0.5"
+features = [ "v4" ]
+
+[dependencies.finito]
+path = "../finito-core"