Improvement proposal: "LoggerForType", use phantom types to disambiguate loggers

[gbogard]

Hello :)

As someone else pointed out in this issue #397, the class that shows up in traces reflects where the logger was instantiated, usually the main class of the application. In many applications, it is however desirable to have several loggers, each with a name reflecting a particular portion of code. This makes it easier to spot where an issue comes from, and allows logging backends to be configured on a per-class basis.

However, creating multiple loggers and passing them around can be a rather frustrating experience. Having multiple loggers means you have to give up using implicits to pass them around. I came up with a solution to address this issue, and believe this could be a nice improvement for this library.

The idea is to use a phantom type to bind a logger instance to a single class, and optionally use a ClassTag to conveniently instantiate named loggers. There are code examples in the repository :)

final case class LoggerForType[F[_], T](logger: Logger[T]) extends Logger[F]

I haven't yet published the work as a library, and I am willing to open a PR to include it directly in log4cats, if the maintainers find it desirable :)

Cheers, and thank you for your work