Fix memory bug - Added empty array as default param

- Fix a critical memory management bug that occurs when returning a
member from a method that needed local variables, because
ZEPHIR_MM_GROW() was called but ZEPHIR_MM_RESTORE() was not.
- Added empty array as possible default parameter to methods. For
instance:
public function mymethod(myParam = [])
- Added getParameter($name) to CommandInterface
Merge pull request #35 from mobli/master

Fix critical memory bug - Fix detecting null params - Added empty array as default param