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

test/integrationtests/adaptor-glue.h

@@ -82,6 +82,16 @@ protected:
             return this->sumVectorItems(a, b);
         });
 
+        object_.registerMethod("doOperationSync").onInterface(INTERFACE_NAME).implementedAs([this](uint32_t param)
+        {
+            return this->doOperationSync(param);
+        });
+
+        object_.registerMethod("doOperationAsync").onInterface(INTERFACE_NAME).implementedAs([this](sdbus::Result<uint32_t> result, uint32_t param)
+        {
+            this->doOperationAsync(param, std::move(result));
+        });
+
         object_.registerMethod("getSignature").onInterface(INTERFACE_NAME).implementedAs([this](){ return this->getSignature(); });
         object_.registerMethod("getObjectPath").onInterface(INTERFACE_NAME).implementedAs([this](){ return this->getObjectPath(); });
 
@@ -139,6 +149,8 @@ protected:
     virtual sdbus::Struct<std::string, sdbus::Struct<std::map<int32_t, int32_t>>> getStructInStruct() const = 0;
     virtual int32_t sumStructItems(const sdbus::Struct<uint8_t, uint16_t>& a, const sdbus::Struct<int32_t, int64_t>& b) = 0;
     virtual uint32_t sumVectorItems(const std::vector<uint16_t>& a, const std::vector<uint64_t>& b) = 0;
+    virtual uint32_t doOperationSync(uint32_t param) = 0;
+    virtual void doOperationAsync(uint32_t param, sdbus::Result<uint32_t> result) = 0;
     virtual sdbus::Signature getSignature() const  = 0;
     virtual sdbus::ObjectPath getObjectPath() const = 0;
     virtual ComplexType getComplex() const = 0;