Doc: Various fixes to Qt Audio Engine documentation

-fixed \since to "\since 5.0" (Qt version 5.0)
-made a \qmlmodule page so the list of related classes are automatically
 listed
-made changes in the Qt Multimedia documentation to link to the
 Qt Audio Engine documentation

Change-Id: Ibdd3da02871648988a73172934e684840c4ce0ae
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>

src/imports/audioengine/qdeclarative_sound_p.cpp

@@ -140,10 +140,10 @@ void QDeclarativeSoundCone::componentComplete()
 /*!
     \qmltype Sound
     \instantiates QDeclarativeSound
-    \since 1.0
+    \since 5.0
     \brief Define a variety of samples and parameters to be used for
     SoundInstance.
-    \inqmlmodule QtAudioEngine 1.0
+    \inqmlmodule QtAudioEngine
     \ingroup multimedia_audioengine
     \inherits Item
     \preliminary