feat: Implement signature-specifc reference

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.

src/generic/divide.mjs

@@ -0,0 +1,4 @@
+export const divide = {
+   'any,any': ({multiply, invert}) => (x, y) => multiply(x, invert(y))
+}
+