add extended tracer module

[zeitlinger]

The Opentelemetry APIs are rather difficult to use - therefore I've developed the following utility method, which is part of a company internal library - so it has already been tested by some users.

Based on this PR, I'm now creating a PR here.

[zeitlinger]

@trask I hope this PR makes more sense now - I've kept the idea of being able to wrap a Tracer - but I've also kept the static methods in the Tracing class.

[trask]

I'm a little hesitant to introduce too much syntactic sugar on top of opentelemetry-api, since that creates more ways to do the same thing, which could cause confusion

at the same time, it makes sense to have somewhere to experiment with things that we might want to add into the opentelemetry-api itself

we also have opentelemetry-instrumentation-api, which possibly has a little bit of overlap

I left a couple of initial comments, overall I think it might help to pair the PR down and just focus on the Tracing class at least initially

[zeitlinger]

we also have opentelemetry-instrumentation-api, which possibly has a little bit of overlap

I checked Instrumenter but didn't see anything that could be reused.

I left a couple of initial comments, overall I think it might help to pair the PR down and just focus on the Tracing class at least initially

I like that idea and have adjusted the PR accordingly 😄

[zeitlinger]

@trask @jkwatson @jack-berg as discussed yesterday, I've removed GlobalTracer, injected Tracer into Tracing, and added before/after examples.

[zeitlinger]

@trask build is passing now 😄

[trask]

thanks @zeitlinger for your patience and incorporating all the feedback!