Allow just a plain function for when there are no dependencies,
and allow an object with 'uses' and 'does' properties for the
dependencies (optional) and implementation, respectively.
Also starts each PocomathInstance with no types at all, and uses the new
situation to eliminate the need for a Complex "base case".
Resolves#14.
Resolves#13.
Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Reviewed-on: #15
