Promises/A+ passing

Note: this release passed all the specs but had an infinite recursion bug that meant the compliance suite never quit. Therefore, this release did not truly pass Promises/A+.

Passing the core Promises/A+ compliance tests. Included are:

• a promise constructor Potential
  • invokes an executor function with resolve and reject parameters
  • returns a new promise
• a deferral factory function Potential.defer()
  • deferrals have resolve and reject methods (which ultimately call the settle method)
  • deferrals are each associated with a unique promise property
• promises have:
  • a .then method to add optional success & error handlers