* lib/rupnp/ssdp/searcher.rb: remove DEFAULT_RESPONSE_WAIT_TIME
  and options[:response_wait_time] management

* lib/rupnp/control_point.rb: add DEFAULT_RESPONSE_WAIT_TIME
  constant and options[:response_wait_time] management.
  Add add_timer in #search_and_listen to finalize search and
  begin listening.

* lib/rupnp/ssdp.rb: add SSDP.listen

* lib/rupnp/ssdp/listener.rb: create a listener.
Replace eventmachine by eventmachine-le (cannot set a UDP server
with eventmachine)
Rename SSDP::HttpResponse to SSDP::Http
* lib/rupnp/device.rb: add #expiration attr_reader
* lib/rupnp/control_point.rb, lib/rupnp/ssdp/listener.rb:
  Manage SSDP notifications (NOTIFY). ssdp:alive and ssdp:byebye
  are managed.