Identify functions - self, always false, always empty, etc

[coolaj86]

• Function._noop does nothing (return is not defined)
• String._empty returns an empty string
• Boolean._false always returns false
• Boolean._true always returns true
• Boolean._invert always returns the opposite
• Object._self always returns the input
  (an identity function like Object itself, but for all types)
• Object._null always returns null

There are other functions that make sense to include, but that I don't think I've actually found use for:

• Number._zero
• Is Boolean._false redundant with Function._noop?

Function._noop = function () {};
Boolean._false = function () { return false; };
Boolean._true = function () { return true; };
Object._self = function (val) { return val; };