feat: config and approximate equality (#19)

Establishes a global config object for a TypeDispatcher instance, so far
  with just properties representing comparison tolerances. Begins a
  "relational" group of functions with basic approximate equality, and
  an initial primitive ordering comparison. Ensures that methods that
  depend on properties of `config` will be properly updated when those
  properties change.

Reviewed-on: #19
Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Co-committed-by: Glen Whitney <glen@studioinfinity.org>

src/number/helpers.js

@@ -6,4 +6,11 @@ import {Returns} from '#core/Type.js'
 export const plain = f => onType(
    Array(f.length).fill(NumberT), Returns(NumberT, f))
 
-export const boolnum = Returns(NumberT, p => p ? 1 : 0)
+// Takes a behavior returning boolean, and returns a factory
+// that returns that behavior if the boolean type is present,
+// and otherwise wraps the behavior to return 1 or 0.
+export const boolnum = behavior => math => {
+    const {BooleanT} = math.types
+    if (BooleanT) return Returns(BooleanT, behavior)
+    return Returns(NumberT, (...args) => behavior(...args) ? 1 : 0)
+}