Text: updated and fixed Renderer docs.

Thanks again, @wivlaro.

src/Magnum/Text/Renderer.h

@@ -176,20 +176,22 @@ methods, returning result either as data arrays or as fully configured mesh.
 The text can be then drawn as usual by configuring the shader and drawing the
 mesh:
 @code
-Text::AbstractFont* font;
+// Font instance, received from plugin manager
+std::unique_ptr<Text::AbstractFont> font;
+
+// Configured glyph cache
 Text::GlyphCache cache;
 
-Shaders::VectorShader2D shader;
+Shaders::Vector2D shader;
 Buffer vertexBuffer, indexBuffer;
 Mesh mesh;
 
-// Render the text
-Range2D rectangle;
-std::tie(mesh, rectangle) = Text::Renderer2D::render(*font, cache, 0.15f,
-    "Hello World!", vertexBuffer, indexBuffer, BufferUsage::StaticDraw);
+// Render the text, centered
+std::tie(mesh, std::ignore) = Text::Renderer2D::render(*font, cache, 0.15f,
+    "Hello World!", vertexBuffer, indexBuffer, BufferUsage::StaticDraw, Text::Alignment::LineCenter);
 
-// Draw white text centered on the screen
-shader.setTransformationProjectionMatrix(projection*Matrix3::translation(-rectangle.width()/2.0f))
+// Draw the text on the screen
+shader.setTransformationProjectionMatrix(projection)
     .setColor(Color3(1.0f))
     .setVectorTexture(glyphCache->texture());
 mesh.draw(shader);
@@ -202,19 +204,19 @@ While this method is sufficient for one-shot rendering of static texts, for
 mutable texts (e.g. FPS counters, chat messages) there is another approach
 that doesn't recreate everything on each text change:
 @code
-Text::AbstractFont* font;
+std::unique_ptr<Text::AbstractFont> font;
 Text::GlyphCache cache;
-Shaders::VectorShader2D shader;
+Shaders::Vector2D shader;
 
 // Initialize renderer and reserve memory for enough glyphs
 Text::Renderer2D renderer(*font, cache, 0.15f);
-renderer.reserve(32, BufferUsage::DynamicDraw, BufferUsage::StaticDraw);
+renderer.reserve(32, BufferUsage::DynamicDraw, BufferUsage::StaticDraw, Text::Alignment::LineCenter);
 
 // Update the text occasionally
 renderer.render("Hello World Countdown: 10");
 
-// Draw the text centered on the screen
-shader.setTransformationProjectionMatrix(projection*Matrix3::translation(-renderer.rectangle().width()/2.0f))
+// Draw the text on the screen
+shader.setTransformationProjectionMatrix(projection)
     .setColor(Color3(1.0f))
     .setVectorTexture(glyphCache->texture());
 renderer.mesh().draw(shader);