The listenTo callback is now accessible off the flux object for use outside the angular lifecycle (e.g. React). It returns an unsubscribe callback that can be invoked upon cleanup of the component.
Updated the package to use rollup so it is compatible as an ES6 import, UMD module, or common module. Only breaks backward compatibility with 3.x if code was explicitly referencing release/flux-angular.js instead of importing the normal way.