Added GraphicsContextBase, which acts as the foundation of all IGraphicsContext implementations.
Added DesktopGraphicsContext, which acts as the foundation of all desktop (i.e. not ES) IGraphicsContext implementations.
Modified all IGraphicsContext implementations to inherit from GraphicsContextBase and/or DesktopGraphicsContext.
Removed OpenTK.Graphics.Glu class (reason: deprecated upstream; most functionality provided by OpenTK math; not compatible with OpenGL 3.0+.) OpenTK.Graphics.Glu can be accessed through OpenTK.Compatibility.
Added OpenGL|ES-specific ErrorHelper classes.
Moved OpenTK.Graphics.DisplayDevice and OpenTK.Graphics.DisplayResolution to the root OpenTK namespace (reason: their functionality is not specific and does not depend on OpenTK.Graphics).
Split Graphics*Exception classes into different files.
Made GraphicsErrorException public (reason: necessary for OpenTK.Compatibility).
Improved CreateDummyContext logic to detect and use the context handle of the current thread or a specified handle.
Removed GetCurrentContext() methods from platform-specific context implementations (everything now goes through the relevant IPlatformFactories).
Added GraphicsContext.ErrorChecking property to temporarily disable error checking if necessary.
Error checking is now added to all functions in debug mode (the generator would miss specific CLS-compliant overloads before).
Added OpenGL 3.0 support for GLX contexts.
Added support for creating dummy contexts (useful if you are creating contexts from an external library).
Cleaned up unused and stale code.