Start porting notes section from 1.6 to current master.

Docs/Urho3D.dox

@@ -1029,6 +1029,9 @@ From 1.5 to 1.6:
 - Build system - the inclusion of Urho3D-CMake-common.cmake module into downstream project's CMakeLists.txt would implicitly instruct CMake to find all the required software packages, including Urho3D library. There is no need now for downstream's CMakeLists.txt to call "find_package (Urho3D)" explicitly, to avoid the Urho3D library from being searched twice. The enhanced FindUrho3D.cmake module now auto-discovers the build options used when building Urho3D library and reapply them to downstream projects. There is no need for users to remember and to supply the same set of build options when performing the initial configuration/generation of the downstream project's build tree.
 - Build system - the Urho3DAll.h header file is now auto-generated for downstream project that needs it. It is not a good practice though to use this "convenience header" as it would slow down the build process unnecessarily.
 
+From 1.6 to master:
+
+- SoundSource autoremove boolean was replaced with AutoRemoveMode enum, which allows removing either the component or owner node. Also used by ParticleEmitter.
 */
 
 }