Query, Explain and Cancel are going throught the asyncdbconnection now.

Todo: Notice processing and error reporting.

PgsqlConn.h

@@ -129,15 +129,17 @@ namespace Pgsql {
 
 	class Canceller {
 	public:
+		Canceller() = default;
 		Canceller(PGcancel *c);
 		Canceller(const Canceller&) = delete;
 		Canceller& operator=(const Canceller&) = delete;
 		Canceller(Canceller&& rhs);
 		Canceller& operator=(Canceller&& rhs);
 		~Canceller();
-		void cancel();
+
+		bool cancel(std::string *error);
 	private:
-		PGcancel *m_cancel;
+		PGcancel *m_cancel = nullptr;
 	};
 
 
@@ -187,12 +189,16 @@ namespace Pgsql {
 		}
 
 		bool sendQuery(const char * query);
+		bool sendQuery(const std::string &command)
+		{
+			return sendQuery(command.c_str());
+		}
 		bool sendQuery(const QString &command)
 		{
 			return sendQuery(command.toUtf8().data());
 		}
 
-		std::unique_ptr<Result> getResult();
+		std::shared_ptr<Result> getResult();
 
 		bool consumeInput();
 		bool isBusy();