Publish UMD bundle to flight-umd

Fix #210 

This adds the umd bundle (minified too) to the [flight-umd](https://github.com/flightjs/flight-umd) repo when you `make release`. This should also allow us to migrate to commonjs in this repo without a major version bump.

Pre-merge tasks:

- [x] Ensure #293 and #294 have been merged.
- [x] Add all existing tagged releases starting from 1.0.0 to flight-umd. Reference: https://github.com/flightjs/flight/tags
- [x] Relevant README updates.

Post-merge tasks:

- [ ] Unregister 'flight' on bower, re-register using flight-umd git endpoint: https://github.com/bower/bower/issues/120