Port ZEND_BIND_GLOBAL optimization
CT bind args before unpack
Implement ZEND_STRLEN optimization
Implement ZEND_TYPE_CHECK optimization
Implement ZEND_DEFINED optimization
Implement call_user_func_array optimization
Add call_user_func optimization
Expose ast via CG(ast)
Fix interning bug
Resolve futher interning issues

Not sure if this is the right way to do it ...
Use arena allocator (currently leaky!)
Fix leaks

Must find a good way to handle constant expressions...