Run tests in browser with testling

Wired in the nodeunit-browser-tap runner to run tests across lots of browsers.  Try it out with

    npm run-script test-browser

Or check testling ci:

[![testling](https://ci.testling.com/hurrymaplelad/forms.png)](https://ci.testling.com/hurrymaplelad/forms)

Two of the test suites are excluded for now

- `test-form` has some server specific tests that blow up in the browser
- `test-validators` has some unicode that will choke testling until one [these](https://github.com/substack/testling/pull/35) [fixes](https://github.com/substack/testling/pull/34) is merged.

Building on [work in browser-forms](https://github.com/hurrymaplelad/browser-forms/issues/7).