Also implements a config object that upon change, lazily invalidates
all operations that access it.
Also allows references to signatures with nonexistent types (which
typed-function does not); they come back as undefined.
Uses these features to implement sqrt for number and complex.
Resolves#7.
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
