src/awgetd.scm: Improve logging.

* src/awgetd.scm: Improve logging.
  (make-msg-formatter): New procedure.
  (fmt-info): New procedure.
  (fmt-debug): New procedure.
  (fmt-error): New procedure.
  (register-sighandlers, add-link, main-loop): Improve logging.
  (debug-message): Remove.