* t/04-search.t: adding more tests to test the search method
* lib/SRU/Client.pm: refactoring the 'search' method to pass the last tests
* t/04-search.t: checking if the structure return by the search method is a SRU::Client::Response::searchRetrieve object
* lib/SRU/Client.pm: adding a new requirement (XML::LibXML)
* lib/SRU/Client.pm: adding a new requirement (SRU::Client::Response::searchRetrieve)
* lib/SRU/Client.pm: refactoring the 'search' method to use the SRU::Client::Response::searchRetrieve class
* lib/SRU/Client.pm: removing a useless requirement