feat(tazjin/finito): Check in my old Rust state-machine library

I dug through my archives for this and found a version that, while
unfortunately not the latest implementation, is close enough to the
real thing to show off what Finito did.

This is a Postgres-backed state-machine library for complex
application logic. I wrote this originally for a work purpose in a
previous life, but have always wanted to apply it elsewhere, too.

git-subtree-dir: users/tazjin/finito
git-subtree-mainline: 0380841eb1
git-subtree-split: b748117225
Change-Id: I0de02d6258568447a14870f1a533812a67127763

users/tazjin/finito/README.md

@@ -0,0 +1,27 @@
+Finito
+======
+
+This is a Rust port of the Haskell state-machine library Finito. It is
+slightly less featureful because it loses the ability to ensure that
+side-effects are contained and because of a slight reduction in
+expressivity, which makes it a bit more restrictive.
+
+However, it still implements the FSM model well enough.
+
+# Components
+
+Finito is split up into multiple independent components (note: not all
+of these exist yet), separating functionality related to FSM
+persistence from other things.
+
+* `finito`: Core abstraction implemented by Finito
+* `finito-door`: Example implementation of a simple, lockable door
+* `finito-postgres`: Persistent state-machines using Postgres
+
+**Note**: The `finito` core library does not contain any tests. Its
+coverage is instead provided by the `finito-door` library, which
+actually implements an example FSM.
+
+These are split out because the documentation for `finito-door` is
+interesting regardless and because other Finito packages also need an
+example implementation.