animation: Prototype a way of handling state and applying it separately

Handling visibility state ad-hoc has shortcomings in testability and locality, and this module attmepts to rectify that by creating an explicit state machine, along with a loop to drive it.

Actually applying state is not implemented here.

src/lib.rs

@@ -19,6 +19,7 @@ extern crate xkbcommon;
 mod logging;
 
 mod action;
+mod animation;
 pub mod data;
 mod drawing;
 pub mod float_ord;