QmlJS: Add documentation for QmlJS::Value.

Also:
* Remove unnecessary QmlJS:: qualifications in existing documentation.
* Remove unnecessary explicit links in the documentation.

Change-Id: Icb41941d98b5cfe9d2fb3b3887fafee16635eb13
Reviewed-by: Leandro Melo <leandro.melo@nokia.com>

src/libs/qmljs/qmljslink.cpp

@@ -126,7 +126,7 @@ public:
 /*!
     \class QmlJS::Link
     \brief Creates a Context for a Snapshot.
-    \sa QmlJS::Context QmlJS::Snapshot
+    \sa Context Snapshot
 
     Initializes a context by resolving imports. This is an expensive operation.