Type conversion/coercion

Functional programming utility functions

Seeded random functions, mirroring those from clojure core. Each take a
seed, a java.util.Random rng, as first arg. This will be mutated.

Make selections from different sources, using either weighted or
non-weighted random selection, with optional repeatability using
controlled seeds.

Transformation utility functions.
- `restructure` to rewrite maps
- `val-map` map functions over map values