Shore up browser support

[hurrymaplelad]

browser-forms depends on newer APIs like querySelector.

1. Document which potentially unsupported APIs are used, so developers can roll their own polyfills.
2. Add a reference polyfill that can be separately included if rapid old browser support is desired.
3. Use the polyfill to run tests across browsers.
4. Document browser support with and without polyfills.

[ljharb]

I recommend using Testling and a TAP-compatible test harness (like tape) to automate a wide variety of browser testing.

[hurrymaplelad]

I'll check it out, thanks @ljharb, James plugged Testling at his MDD talk. Twice in a week, must be something to it :)

[hurrymaplelad]

Dug a bit into running the suite on Testling. There's a bit of work to do to report browser nodeunit tests via TAP. Feeling a little locked into nodeunit to share tests of the forms core. @ljharb sticking with nodeunit for caolan/forms?

[ljharb]

Good question. I definitely want to get https://github.com/caolan/forms on Testling, so either that means making nodeunit TAP-compliant, or switching from nodeunit to a TAP-compliant test framework.

[hurrymaplelad]

@ljharb cobbled together nodeunit-browser-tap after silence on the nodeunit issue.

Next step is getting browser-forms test running on testling. Should work for vanilla forms tests too if you're interested. Want a PR?

[ljharb]

@hurrymaplelad A PR would be awesome, thanks! I still will need forms' owner to hook up the Testling hook, but I can easily make sure it works on my fork in the meantime.