Add support for the Trace API

[taktoa]

Documented here. It seems very nice for profiling distributed applications; see the attached screenshot. You could have a monad transformer that allows you to easily create regions that are traced.

[iand675]

Hi @taktoa, this is in development on the apm branch. I use it in production at work. Feel free to submit PRs or bug reports if you use it and run into problems!

[symbiont-sam-halliday]

I noticed that you're using JSON in the apm branch but the datadog agent has already moved to using msgpack. You're welcome under the LICENSE to pick the bits from https://github.com/symbiont-io/haskell-datadog (note that we're waiting on an upstream release of msgpack to fix an issue with number precision, so using a source dependency until then).

[felixmulder]

Hey @iand675 - we'd be super interested to use this as well at work. Do you think there'd be a hackage release at some point with the APM branch?

Just wanted to encourage you, thanks for a great lib!