Add logr implementation to README and json.RawMessage to Fields()

[hn8]

Add the fastest (fewest allocation) logr implementation using zerolog, much faster than zapr. Use type switch instead Fields() to avoid map overhead (even with sync.Pool).

[rs]

What is the advantage of having this implementation inside zerolog instead of as a separate project like all other implementations of this interface? I'm generally against adding dependencies, unnecessary complexity or any code that could be implemented outside the library unless there is a good reason.

As I would not be the maintainer of this implementation, I believe it would be better living in a repository you own.

[hn8]

@rs No problem. The existence of log/journald/pkgerrors was my motivation to contribute to zerolog, to have simple subpackages to integrate with other popular libraries. I was trying to optimize go-logr/zapr first, and it turns out zerlog is the fastest implementation for logr after some tuning. IMHO, many Go projects want to keep their logging interface generic (like logr) for library consumers.

[rs]

To be honest, I should have refused journald and pkgerrors.

I'm all for pointing to other projects like logr wrapper in the README. I prefer people composing the right set of libraries for their needs rather than big libraries with hundreds of dependencies to fulfill all the possible needs they will probably never have :)

[hn8]

@rs I reverted logr subpackage and added to README instead as you suggested. Also revert type switch but only add json.RawMessage to Fields() as the minimal change for you to review. I really admire your work and hope that you change your mind one day on hosting logr wrapper since zerolog is definitely the best one. It is funny that neither zerolog nor logr is willing to host the zerolog-logr wrapper, but it is understandable. Just a little bit more hassle for developers like us to use a third-party like mine (I have zero intention for self-promotion). Thanks for your clear communication, appreciate your time and great work!