Fixing doxygen layout for ISceneNode. Same should probably be done throughout.
Our current member function documentation look often rather strange. The reason is that the first 
line in multi-line comment is handled special (it get's a box around it). So in the cases where we use
this for \param or have sentences starting in that line and continuing in the next it always looks broken.
Please click for example through IGUIElement documenation which is not yet fixed to see this.
Also links to enums don't seem to need @ref but just ::my_enum_name.  


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4746 dfc29bdd-3216-0410-991c-e03cc46cb475