Validator async

[ball6847]

As requested in #87 . I've cleaned up my branch and add more detail in README.

Not sure if writing tests is neccessary since this feature depends on angular's $asyncValidators.

Thanks,
Porawit Poboonma

[Jakobovski]

This looks great. Thanks for the hard work!

A few small changes are needed before I merge:

1. Remove the first line from the readme
2. Update the version in bower.json and tag the repo with the new version.
3. Create a new plunkr with the updated code, and update the link in the readme to the plunkr.

Cheers.

[Jakobovski]

Hey any updates on this?