Various tweaks

Sorry for a pull request with a bunch of unrelated stuff in it!

Each commit has a message which should describe the thoughts behind it. The final commit (0447b18) is the one I'm least sure and would be interested to discuss if you think it's a good idea or not.

I'm just leaving the office now so sorry I haven't given all of the information here. I will try to add to it tomorrow if there is anything that needs clarification!
True! I'm building something which targets Chrome on Android so I didn't do any cross-browser testing and there was no mention of this being Chrome only in the article I was reading...

It looks like Firefox should support `getVideoTracks` ([ref](https://developer.mozilla.org/en-US/docs/Web/API/MediaStreamTrack)) but my copy (v31 on OSX) doesn't!

I'll tweak the API and example so it's clear that this will only work on certain browsers for now...