refactor: move TodoMVC example into example/ directory

- example/todomvc/pocketbook/todomvc.cljs — app source
- example/todomvc/todomvc.html — page
- example/todomvc/js/ — compiled output (gitignored)

Server static file serving is now filesystem-based via --static-dir
flag instead of classpath resources. No static dir by default (API
only); bb server passes --static-dir example/todomvc.

Removed resources/public/ — library has no bundled static assets.

.gitignore

@@ -3,6 +3,7 @@
 target/
 out/
 resources/public/js/
+example/todomvc/js/
 *.db
 *.db-shm
 *.db-wal