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/generic/utils.js

@@ -0,0 +1,13 @@
+import {ReturnsAs} from './helpers.js'
+import {onType, ResolutionError} from '#core/helpers.js'
+import {Returns} from '#core/Type.js'
+import {Any} from "#core/TypePatterns.js"
+
+export const isZero = (math, [T]) => {
+   if (!T) { // called with no arguments
+      throw new ResolutionError('isZero() requires one argument')
+   }
+   const z = math.zero(T)
+   const eq = math.equal.resolve([T, T])
+   return ReturnsAs(eq, x => eq(z, x))
+}