lib/solr4r/request.rb (make_request): Set request body if string (XML).
lib/solr4r/builder.rb (to_xml): Replace illegal characters.
lib/solr4r/response.rb (success?): New method.
lib/solr4r/client.rb (add_batch): New method.
lib/solr4r/client.rb (query_string): New method.
lib/solr4r/client.rb (json_query): Use #query_string method.