This reorganizes the layers of abstraction in the sense how `Message` depends on `Connection` and vice versa. Now, `Message` has a link to the `Connection`. This replaces the shortcut link to the low-level `SdBus` interface that the `Message` kept. The interactions from `Message` now go through `Connection` which forwards them to `SdBus`. `Connection` is now a sole owner of the low-level `SdBus` interface. This allows for future changes around `SdBus` (e.g. a change from virtual functions back to non-virtual functions) without affecting the rest of the library. `Proxy`s and `Object`s can now send messages directly without having to go through `Connection`. The `Connection` no more depends on `Message` business-logic methods; it serves only as a factory for messages.
The flow for creating messages: `Proxy`/`Object` -> `Connection` -> `SdBus`
The flow for sending messages: (`Proxy`/`Object` ->) `Message` -> `Connection` -> `SdBus`
This also better reflects how dependencies are managed in the underlying sd-bus library.
Additionally, `getSdBusInterface()` methods are removed which was anyway planned, and improves the design by "Tell, don't ask" principle.
This refactoring is the necessary enabler for other upcoming improvements (regarding sending long messages, or creds refactoring, for example).
This introduces strong types for `std::string`-based D-Bus types. This facilitates safer, less error-prone and more expressive API.
What previously was `auto proxy = createProxy("org.sdbuscpp.concatenator", "/org/sdbuscpp/concatenator");` is now written like `auto proxy = createProxy(ServiceName{"org.sdbuscpp.concatenator"}, ObjectPath{"/org/sdbuscpp/concatenator"});`.
These types are:
* `ObjectPath` type for the object path (the type has been around already but now is also used consistently in sdbus-c++ API for object path strings),
* `InterfaceName` type for D-Bus interface names,
* `BusName` (and its aliases `ServiceName` and `ConnectionName`) type for bus/service/connection names,
* `MemberName` (and its aliases `MethodName`, `SignalName` and `PropertyName`) type for D-Bus method, signal and property names,
* `Signature` type for the D-Bus signature (the type has been around already but now is also used consistently in sdbus-c++ API for signature strings),
* `Error::Name` type for D-Bus error names.
In sdbus-c++ v1, new virtual functions (e.g. overloads of existing virtual functions) were always placed at the end of the class to keep backwards ABI compatibility. Now, with v2, these functions are reordered and functions forming a logical group are together.
This improves the D-Bus object API registration/unregistration by making it more flexible, more dynamic, closer to sd-bus API design but still on high abstraction level, and -- most importantly -- less error-prone since no `finishRegistration()` call is needed anymore.
* Add ability to declare property behavior on PropertyChanged signal
* Add support for Method.NoReply annotation (WIP)
* Add support for common annotations/flags
* 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
