doc++: ResourceManager::instance() now returns a reference.

Signed-off-by: Squareys <Squareys@googlemail.com>

doc/debug-tools.dox

@@ -65,7 +65,7 @@ DebugTools::ResourceManager manager;
 SceneGraph::DrawableGroup3D debugDrawables;
 
 // Create renderer options which will be referenced later by "my" resource key
-DebugTools::ResourceManager::instance()->set("my",
+DebugTools::ResourceManager::instance().set("my",
     DebugTools::ObjectRendererOptions().setSize(0.3f));
 
 // Create debug renderer for given object, use "my" options for it. The

src/Magnum/DebugTools/ForceRenderer.h

@@ -90,7 +90,7 @@ See @ref debug-tools-renderers for more information.
 
 Example code:
 @code
-DebugTools::ResourceManager::instance()->set("my", DebugTools::ForceRendererOptions()
+DebugTools::ResourceManager::instance().set("my", DebugTools::ForceRendererOptions()
     .setScale(5.0f)
     .setColor(Color3::fromHSV(120.0_degf, 1.0f, 0.7f));
 

src/Magnum/DebugTools/ObjectRenderer.h

@@ -75,7 +75,7 @@ Visualizes object position, rotation and scale using colored axes. See
 Example code:
 @code
 // Create some options
-DebugTools::ResourceManager::instance()->set("my", DebugTools::ObjectRendererOptions().setSize(0.3f));
+DebugTools::ResourceManager::instance().set("my", DebugTools::ObjectRendererOptions().setSize(0.3f));
 
 // Create debug renderer for given object, use "my" options for it
 Object3D* object;