Add support for unreliability (with parameters dictionary)

[pthatcherg]

Via a dictionary with RTCQuicStreamParameters.reliable passed to createSendStream.

[aboba]

@pthatcherg Personally, I like this approach better, because there may be other parameters needed in future.

[aboba]

"sent unreliably" should probably be changed to "sent with no retransmissions".

[aboba]

@pthatcherg Also, there is various text in the document that indicates that only reliable streams are supported. So that text also needs to be updated.

[pthatcherg]

Notes to self:

1. Go with parameter to approach (close Add support for unreliability (with an attribute) #74)

2. Consider calling it "disableRetransmissions"

3. Add an example and a paragraph about how this intended to be used (with many small unidirectional streams).

[pthatcherg]

OK, I renamed it, removed the "we don't do unreliable" text in other places, and added an example.