Replace deprecated __defineGetter__/__defineSetter

Use `Object.defineProperties` instead
Fixes #64

* remove-deprecated-define-getter-setter:
  Check that hook redefinition includes hook name in raised exception
  Minor grammar correction in test notice
  Add TODO for v0.7
  Test that an exception should be thrown if setter already exists
  Remove obsolete checking for preexisting setters
  Replace deprecated  `__defineGetter__` and `__defineSetter__` syntaxes.