Tracing SDK living notes

[primiano]

There are 3 different but maybe overlapping problems that we need to address at some point:

1. metadata-like things that we need to interpret other data, e.g. GPU counter names, or package list. What we could have is an implicit __metadata buffer (we need target_buffer by name, not just by index at that point), so data sources could create a TW to target that and append there.

2. Counters/state changes with Initial state (e.g. screen state) we want to remember the last state (and timestamp) before the change… but then in the trace becomes a ProtoVM like problem where we want to remember the last value that fell out of the buffer, not the first one. Should we use protovm or something similar? primiano thinks we should special-case TrackEvent in traced for this sort of stuff and that this is a track-event-like problem

3. Intern-like problems, where things show up and we want to keep referring to them. Should we use protovm or something similar? should we introduce the notion of a "transaction of packets" (similar to the bundle concept in ftrace) where we repeat stuff? TBD