Suggestion to improve logging support

[prikha]

Basic Info

I am concerned about the usability of request/response logging. At the moment one should override the logging middleware like that:

Faraday::Response.register_middleware logger: -> { FaradayMiddlewares::MyLogger }

And then you have to deal with the inheritance. For example you want to change the request logging - then you have to skip using super and bring code from Faraday::Response::Middleware#call to it(To avoid duplicate logging for example). As of super would call a method from Faraday::Response::Logger and then it would propagate to Faraday::Response::Middleware.

Dealing with logging requests/response in faraday is non-transparent(for me at least). I have a suggestion(backed up by some code: #889) of separating log formatter from the logging middleware.

E.g. I would be happy to provide my formatter to the connection configuration:

conn = Faraday.new(:url => 'http://sushi.com/api_key=s3cr3t') do |faraday|
  faraday.response :logger, logger,   formatter: MyFormatter
end

That could be inherited from the base formatter with something like 2 methods to override: request and response.

Steps to reproduce

To see the issue I would recommend an exercise: integrate a structured logger(like SemanticLogger) or at least convert a multiline logging to a one-line-per-request(supporting bodies logging)