Fix sRGB support, now when initialising a Renderer you can explicitly
choose whether to output colors in linear or sRGB color spaces.
Fix examples to show how to render these properly.
Fix comments in examples
There are now only two renderers (only generic over the GL context)
- `AutoRenderer` which is both the old `OwningRenderer` and also
sets up a `SimpleTextureMap` automatically
- `Renderer` which borrows both the GL context and the texture map
on every call to Render
This means the `RendererBuilder` can be entirely removed.
Also `TrivialTextureMap` renamed to `SimpleTextureMap`.
