src/awgetd.scm: Simplify the design.

* src/awgetd.scm: Simplify the design.
  (setup-logging): Use the global instance of awgetd.
  (set-awgetd!): New procedure.
  (run): Likewise.  Rename to `run-awgetd', all callers updated.
  Call `setup-logging' here.
  (daemonize): Likewise.
  (stop): Likewise.
  (register-sighandlers): Likewise.
  (create-pid-file): Likewise.
  (remove-pid-file): Likewise.
  (open-socket): Likewise.
  (close-socket): Likewise.
  (aworker-main-loop): Likewise.
  (start-aworker): Likewise.
  (main-loop): Likewise.
  (add-link): Don't take awgetd instance as a parameter.
  (rem-link): Likewise.
  (send-message): Likewise.
* src/awget.scm (daemonize): Set the default instance of the
  awgetd.