Support for Zemax like optical descriptions?

[mattngc]

Seems like quite a few users would be interested in trying their Zemax optical models in Raysect. Its very unlikely this could ever be a 1-1 match, i.e. load a Zemax file and ray-trace it in Raysect. But it might be possible to provide some migration tools. For example, we might provide a set of objects / functions that can convert a set of sequential optics instructions into a Raysect scene-graph. This would be fairly easy through relative scene-graph operations.