* lib/rupnp.rb: add RUPNP.logdev= and RUPNP.logdev to manage a
  common log device for this library.
* lib/rupnp.rb:
  Add RUPNP.log_level= and RUPNP.log_level.
Add log  facility

* lib/rupnp/log_mixin.rb: Mixin for loggin.
* lib/rupnp/base.rb, lib/rupnp/control_point.rb,
  lib/rupnp/device.rb, lib/rupnp/ssdp.rb,
  lib/rupnp/ssdp/multicast_connection.rb,
  lib/rupnp/ssdp/searcher.rb;
  Use loging facility LogMixin.log instead of puts.
* lib/rupnp/service.rb:
  Add messages on fail from Service.
  Add test to check sanity of SCPD.

* lib/rupnp/device.rb:
  service.errback: add msg block parameter to log reason of
  failure.