Add Number polyfills

This adds the following ES6 Number functions/constants:

  MAX_SAFE_INTEGER
  MIN_SAFE_INTEGER
  EPSILON
  isFinite
  isInteger
  isNaN
  isSafeInteger
We could verify that
(1 + EPSILON) - 1 === EPSILON
and
(1 + (EPSILON/2) - 1) === 0