Tracing Support

[mattludwigs]

Let's remove logging from Mobius, but provide a higher level trace API so that if we need to debug some aspects of Mobius we can from an IEx console.

[ewildgoose]

But what do we want to trace?

Do bear in mind that logging and metrics are all implemented through the Logger system, so you probably also want the tracing system to be implemented similarly?

Phoenix and some other libs allow configuring logging levels as part of their arguments. Technically it can also be done through configuring Logger and some other magic, but in my opinion this is not well documented and quite a hassle.

I think broadly logging in response to specific function calls is kinda fine. However, background task logging quickly becomes tiresome when working with IEX because it interrupts what you are typing. There are solutions to this of course, but the basic philosophy I think defines how we might try and define a tracing API

Note that the erlang tracing stuff is excellent, so perhaps whatever you want here can be implemented with some wrappers around that to make it easy to turn on/off?