[Parse] implement impact & execute callbacks

`parse_effects()` now accepts functor arguments with the signature `void F( parse_callback_e )`
* `PARSE_CALLBACK_PRE_IMPACT` will run the callback before action_t::impact()
* `PARSE_CALLBACK_POST_IMPACT` will run the callback after action_t::impact()
* `PARSE_CALLBACK_POST_EXECUTE` will run the callback after action_t::execute()

`EXPIRE_BUFF` argument to `parse_effects()` will create a callback that expires the buff after execute()
`DECREMENT_BUFF` argument to `parse_effects()` will create a callback that decrements the buff after execute()