built-in tracing support

[jbg]

Is there any interest in built-in tracing (formerly tokio-trace) support? I'm looking at how to instrument the queries my application (which is already using tracing) makes and without built-in support in rust-postgres I will need to construct wrappers and modify deadpool to return those wrappers, which gets a bit untidy.

[sfackler]

Sure, I'd be happy to take a PR!

[ar3s3ru]

I'd love that too! You could put the wrappers behind a feature flag that is not enabled by default, so deadpool doesn't "break" and users uninterested in the traces can just opt-out of the dependency.