Moved SoundData and SoundFormat to OpenTK.Compatibility.
Moved AL and Alc classes to OpenTK.Audio.OpenAL and added the previous namespace to OpenTK.Compatibility.
Removed SoundData wrappers from AL class.
Updated samples to use the new API.
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).