Rough draft of EME Concerns document.

As discussed in various forums, this is a version of the opinion document that tries to catalog our concerns for EME as a web-facing API, without suggesting solutions or focusing on specific technical choices or problems with the current mechanism. Feedback definitely welcome.

I understand this idea, but (a) Extensible Web principle sooner or later will bring possibility to access raw video data, thus making possible writing codecs in pure JS, which makes an entire argument useless; (b) I certainly don't like current codecs situation and I'd prefer to put forward a requirement for every EME protocol and format to be free and open.