Typos and debugging. No functional changes.

It's working!
Module wrap and add missing arrayIndex var
Typo fix
Break out DOM sub support from Y.on()
Manual tests
Make sub methods return Subscriptions + more

* on(), after(), and subscribe() return Subscriptions
* Subscription(arrayOfSubs) now works for batched subs
* bubblePath is lazily created
* CustomEvent.proto.fire() restructured to be smarter about fireOnce events
  and events with defaultFn when short circuiting.
* Various text changes, and code cleanup
Consolidate eventx, eventx-dynamic, and eventx-y

eventx-y was so small, it begged to be included in eventx, but required
eventx-dynamic, which isn't tiny, but not so big that it convinced me not
to do it.
Merge test_y.html into test.html
Fix typos added with eventx-dynamic and -y merge
Update and add cautionary text
+cancelBubble=true, subscribe returns Subscription