Shaders: update outdated docs about passing stuff to constructors.

There's a Configuration class now.

src/Magnum/Shaders/FlatGL.h

@@ -94,10 +94,10 @@ Common rendering setup:
 @section Shaders-FlatGL-textured Textured rendering
 
 If you want to use a texture, you need to provide also the
-@ref TextureCoordinates attribute. Pass @ref Flag::Textured to the constructor
-and then at render time don't forget to bind also the texture via
-@ref bindTexture(). The texture is multiplied by the color, which is by default
-set to @cpp 0xffffffff_rgbaf @ce. Common mesh setup:
+@ref TextureCoordinates attribute. Pass @ref Flag::Textured to
+@ref Configuration::setFlags() and then at render time don't forget to bind
+also the texture via @ref bindTexture(). The texture is multiplied by the
+color, which is by default set to @cpp 0xffffffff_rgbaf @ce. Common mesh setup:
 
 @snippet MagnumShaders-gl.cpp FlatGL-usage-textured1
 

src/Magnum/Shaders/MeshVisualizerGL.h

@@ -170,10 +170,10 @@ configure the shader.
 @endparblock
 
 The shader expects that you enable wireframe visualization by passing an
-appropriate @ref Flag to the constructor --- there's no default behavior with
-nothing enabled. The shader is a 2D variant of @ref MeshVisualizerGL3D with
-mostly identical workflow. See its documentation for more information,
-workflows that differ are shown below.
+appropriate @ref Flag to @ref Configuration::setFlags() --- there's no default
+behavior with nothing enabled. The shader is a 2D variant of
+@ref MeshVisualizerGL3D with mostly identical workflow. See its documentation
+for more information, workflows that differ are shown below.
 
 @section Shaders-MeshVisualizerGL2D-instancing Instanced rendering
 
@@ -1390,8 +1390,8 @@ shader.
 
 The shader expects that you enable wireframe visualization, tangent space
 visualization or object/primitive ID visualization by passing an appropriate
-@ref Flag to the constructor --- there's no default behavior with nothing
-enabled.
+@ref Flag to @ref Configuration::setFlags() --- there's no default behavior
+with nothing enabled.
 
 @section Shaders-MeshVisualizerGL3D-wireframe Wireframe visualization
 

src/Magnum/Shaders/PhongGL.h

@@ -69,11 +69,11 @@ Common rendering setup:
 
 If you want to use textures, you need to provide also the
 @ref TextureCoordinates attribute. Pass appropriate @ref Flag combination to
-the constructor and then at render time don't forget to also call appropriate
-subset of @ref bindAmbientTexture(), @ref bindDiffuseTexture() and
-@ref bindSpecularTexture() (or the combined @ref bindTextures()). The texture
-is multiplied by the color, which is by default set to fully opaque white for
-enabled textures. Mesh setup with a diffuse and a specular texture:
+@ref Configuration::setFlags() and then at render time don't forget to also
+call appropriate subset of @ref bindAmbientTexture(), @ref bindDiffuseTexture()
+and @ref bindSpecularTexture() (or the combined @ref bindTextures()). The
+texture is multiplied by the color, which is by default set to fully opaque
+white for enabled textures. Mesh setup with a diffuse and a specular texture:
 
 @snippet MagnumShaders-gl.cpp PhongGL-usage-texture1
 
@@ -84,8 +84,8 @@ Common rendering setup:
 @section Shaders-PhongGL-lights Light specification
 
 By default, the shader provides a single directional "fill" light, coming from
-the center of the camera. Using the @p lightCount parameter in constructor, you
-can specify how many lights you want, and then control light parameters using
+the center of the camera. With @ref Configuration::setLightCount() you can
+specify how many lights you want, and then control light parameters using
 @ref setLightPositions(), @ref setLightColors(), @ref setLightSpecularColors()
 and @ref setLightRanges(). Light positions are specified as four-component
 vectors, the last component distinguishing between directional and point