Added initial support for SPL autoload stack with spl_autoload_register()
Fixed issues with namespaced class and function references

- Improved support for string references vs. bareword references,
  ie. `new My\Class()` vs. `$name = 'My\Class'; new $name`
Added support for registering string callables with spl_autoload_register()
Added support for indirectly calling instance methods via arrays

- eg. `$ref = array($object, 'methodName'); $ref(...);`
Added support for calling static methods indirectly via arrays