Return room URI in CreateResponse

[xDarksome]

Continues #165

Background

To be able to properly integrate medea we at social backed also need ability to receive room URI (you call it sid?) as part of CreateResponse.

In current implementation by requesting "create room R with members A and B" we are getting something like:

CreateRespose {
    sid: {
             "A": "ws://127.0.0.1:8080/ws/R/A", 
             "B":"ws://127.0.0.1:8080/ws/R/B" 
         }, 
    error: None
}

But we would like to get:

CreateRespose {
    sid: {
             "R": "ws://127.0.0.1:8080/ws/R"
         }, 
    error: None
}

If such format contradicts with your concepts, this one will also be OK:

CreateRespose {
    sid: {
             "R": "ws://127.0.0.1:8080/ws/R",
             "A": "ws://127.0.0.1:8080/ws/R/A", 
             "B":"ws://127.0.0.1:8080/ws/R/B"
         }, 
    error: None
}

We surely can parse it ourselves, but it would be better if we remain URI format agnostic.

Problem to solve

• Return room URI in CreateResponse

[xDarksome]

@alexlapa @tyranron suggests we just parse it and don't intrude in your design, so changes in the format of URI (sid) should be considered a breaking change.