notecache: add initial in-memory notecache

This is useful for things like relative time strings and other
transient note cache state

Signed-off-by: William Casarin <jb55@jb55.com>

src/lib.rs

@@ -11,6 +11,7 @@ mod filter;
 mod ui;
 mod timecache;
 mod time;
+mod notecache;
 mod frame_history;
 mod timeline;