Now whole Magnum, Magnum::SceneGraph and Magnum::Math namespaces are
fully documented -- each class has at least "getting started"
documentation, larger modules are documented on separate pages.
Some extensions are not part of any core OpenGL version (such as
EXT_direct_state_access, EXT_texture_filter_anisotropic etc.), thus they
have None for core version. Current mechanism in
Context::isExtensionSupported() is that it checks for core version first
and if that is supported, it doesn't check for the extension itself.
Until now Context::isVersionSupported(None) returned always true, which
meant that all non-core extensions were marked as supported
_everywhere_.