[ new ] simple nbe using a fancy-ish domain

The way we manufacture the domain we use as a model for this little
language is obviously inspired by ~/papers/models/. It also relies
heavily on knowledge acquired reading (no ranking here, just listing
them in the order I read them):

- Abel's habilitation thesis
- Filinski and Rohde's Denotational Account of Untyped NBE
- Pitts' Computational Adequacy via Mixed Inductive Definitions