Add non-mirage examples

[Drup]

• [ ] ocamlgraph: Exercise very few features (the external functor hierarchy is very flat and doesn't need connect. switching modules at configure time is not very useful).
• [ ] Extendable interpretor.

[Drup]

A new very interesting example: An extendable interpretor.

[Drup]

It would also be nice to study the various circuit calculus, they sometimes provide similar features.

[Drup]

Also worth studying: the link mixins in backpack: http://research.microsoft.com/en-us/um/people/simonpj/papers/modules/backpack-2016.pdf

[avsm]

https://github.com/ryanrhymes/owl has a big functor stack, but hasnt yet been ported to functoria.

[Drup]

Tada: https://github.com/Drup/functoria-lua !