Should document what RTCRTPStreamStats metrics are valid when isRemote is true.

[taylor-b]

For example:

• targetBitrate isn't something that's communicated via RTCP (to my knowledge), so I imagine it's only valid when isRemote is false.
• roundTripTime, though it uses RTCP RRs for its calculation, is a property of sent streams and thus only valid when isRemote is false.

Also: it would be helpful to have a small summary of how RTCOutboundRTPStreamStats, RTCInboundRTPStreamStats, isRemote and associateStatsId relate to each other. As I understand, each sent stream will provide an RTCOutboundRTPStreamStats where isRemote is false and an RTCInboundRTPStreamStats where isRemote is true. And each received stream will provide an RTCInboundRTPStreamStats where isRemote is false, and an RTCOutboundRTPStreamStats where isRemote is true. Which makes me realize: why do we have separate inbound/outbound stats objects that are associated by ID, instead of just putting everything in one object?

[alvestrand]

The reason why the local sender & remote receiver aren't bundled into one object is that the timestamps will be different (one is from local variables, the other is from the RTCP report reception).

[vr000m]

I believe the changes in #191 fixes this? @jan-ivar @taylor-b WDYT?

[taylor-b]

Agreed, closing.