feat: config and approximate equality

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.

src/core/README.md

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+## Nanomath core
+
+The organization here is to keep the core engine as compact and as agnostic
+as to what sort of functions and types there might be in a TypeDispatcher as
+possible. This division will keep it plausible to break out just the core
+as a TypeDispatcher package that could be used independently for any collection
+of overloaded functions on a universe of types. So we want to place as few
+assumptions/preconditions as to what functions and/or types there will be.
+
+## Core Types
+
+As of this writing, the only two types required to be in a TypeDispatcher are
+Undefined (the type inhabited only by `undefined`) and TypeOfTypes (the type
+inhabited exactly by Type objects).
+
+## Core methods
+
+Similarly, as of this writing the only methods that must be in a TypeDispatcher
+are:
+
+Type
+:   the class (constructor) for Type objects, called via `new Type(...)`.
+    Note that merely constructing a Type does not regeister it within any
+    TypeDispatcher; it must be `.merge()`d into the TypeDispatcher.
+
+typeOf
+: determines the type of any value
+
+merge
+: adds values and methods to the TypeDispatcher
+
+resolve
+: finds values and methods in the TypeDispatcher, by key and types list
+
+Any (other) functions an instance wants to have acting on the core Types
+should be defined elsewhere and merged into the instance.
+
+In nanomath as a whole, rather than within its core, we also assume that
+the NumberT type of regular JavaScript numbers is always present (i.e., no
+need to check if it is in the instance), and we put all functions that we
+want to define on the core Types in the coretypes directory.