Add middleware Raxx.Logger

[CrowdHailer]

This should be started in a new repo and linked from the extensions section of this repo. The hex project should be raxx_logger

• Logger should write a single line if response is sent in a complete state. i.e. when body is false or binary()
• Logger should write a line for first part of response and details of each chunk when response is streamed.
• Logger could use common logger format.
  • it could be customised using: https://www.ibm.com/support/knowledgecenter/en/ssw_i5_54/rzaie/rzaielogformat.htm
  • similar to old implementation here. https://github.com/CrowdHailer/Tokumei/blob/raxx-0.11.1/app/lib/tokumei/common_logger.ex

[CrowdHailer]

Far more complete common logger implementation

[lpil]

Is there an example of the middleware format and usage?