* spec/ssdp/searcher_spec.rb: add dpecs for RUPNP::SSDP::Searcher.

* spec/spec_helper.rb: add a be_a_msearch_packet matcher.

* lib/rupnp/ssdp.rb, lib/rupnp/ssdp/m_search.rb: remove m_search.rb

* lib/rupnp/ssdp/searcher.rb: create M-SEARCH packet without using
  SSDP::M_SEARCH class.