Close generator on return

Add support for executing a zend_execute_data

This adds another function execute_ex(), which accepts a zend_execute_data
struct to run (contrary to execute(), which accepts a zend_op_arr

Add support for executing a zend_execute_data

This adds another function execute_ex(), which accepts a zend_execute_data
struct to run (contrary to execute(), which accepts a zend_op_array from
which it initialized the execute_data).

This needs a bit more cleanup.

show more ...

Add initial code for suspending execution

This is just some initial code, which is still quite broken (and needs to be
moved so it can be reused.)

Add empty Generator class