describe
Usage: describe(spec)
Returns an abbreviated description of the spec as data.
Example:
const s = require('speculaas');
const {isNumber, isString} = s.utils;
s.def('::ingredient', s.cat(':quantity', isNumber, ':unit', isString));
s.describe('::ingredient');
// ['cat', ':quantity', 'isNumber', ':unit', 'isString']