Introduce support for asynchronous server-side methods (#12)

* Add preliminary changes for async server methods

* Refactor the Message concept and break it into distinctive types

* Continue working on async server methods (high-level API mainly)

* Continue developing support for async server

* Finishing async server methods

* Finishing async server methods (fixing tests & cleaning up)

* A little code cleaning

* Add unit tests for type traits of free functions

* Support for generating async server methods in stub headers

* Update ChangeLog for v0.3.0

* Update the tutorial with how to use async server-side methods

* Update the TOC in sdbus-c++ tutorial

* Update numbering in TOC

* Remove unnecessary code

* Final cleanups

src/Makefile.am

@@ -5,6 +5,7 @@ libsdbus_c___la_SOURCES = \
 	Connection.cpp \
 	ConvenienceClasses.cpp \
 	Message.cpp \
+	MethodResult.cpp \
 	Object.cpp \
 	ObjectProxy.cpp \
 	Types.cpp \