More matrix classes

This is a complete set of all the matrix sizes supported by GLSL, both the float and double versions. All basic functionality is implemented, but I haven't done much testing on it.

Additionally, I added the ability to add and subtract matrices and multiply them by scalars.

There's probably a few things here or there that I forgot about (mostly in documentation), I'm planning on going through the vector/matrix classes and fixing all the minor documentation inconsistencies later, but if you want me to include documentation before you pull, that's fine too.

Also I included additional helper methods in `Source/OpenTK/Graphics/OpenGL/GLHelper.cs ` and `/Source/OpenTK/Graphics/ES20/Helper.cs`

Also this pull request solves issue #4.