sdlsample: Added first check-in of a SDL sample that creates an OpenGL
context and can render a triangle.

The goal is to get it to a stage where it can load in a fragment, vertex
and geometry shader.
sdlsample: Added support for loading in a vertex and fragment shader.

The triangle is now coloured blue as per the fragment shader.

The vertex shader simply passes the point unaltered.
sdlexample: Added the ability to load a geometry shader.

The geometry shader at the moment causes the base of the triangle to be
rendered at -0.8 instead of -1.0.
sdlsample: Now send down two points and generate a triangle from each.

This demostrates the use-case of generating a tirnagle from a single
point (x, y, z).