Fix a number of doc errors and warnings.

* Document a few missing classes/functions/methods
* Fix a number of QML snippets that wouldn't work as standalone snippets
* Add files to .pro so they show up in Creator..

Still the mysterious lack of controls dir documentation persists :/

Change-Id: I57162371a4d966e4db5bdb1b71d1baf9c0ca57c3
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>

src/multimedia/audio/qaudio.cpp

@@ -62,7 +62,7 @@ public:
 
 }
 
-/*
+/*!
     \namespace QAudio
     \brief The QAudio namespace contains enums used by the audio classes.
     \inmodule QtMultimedia
@@ -70,7 +70,7 @@ public:
     \ingroup multimedia_audio
 */
 
-/*
+/*!
     \enum QAudio::Error
 
     \value NoError         No errors have occurred
@@ -80,7 +80,7 @@ public:
     \value FatalError      A non-recoverable error has occurred, the audio device is not usable at this time.
 */
 
-/*
+/*!
     \enum QAudio::State
 
     \value ActiveState     Audio data is being processed, this state is set after start() is called
@@ -92,7 +92,7 @@ public:
                            is set after start() is called and while no audio data is available to be processed.
 */
 
-/*
+/*!
     \enum QAudio::Mode
 
     \value AudioOutput   audio output device