Recognize "use parent".

`use base qw(Modules);` has already been recognized by this module. On the other hand, `use parent qw(Modules)` has not yet. `base` is discouraged and `parent` is recommended for ordinary usages as described in POD of `base`. So, I added the code for `parent`.

One concern is how to handle `parent` itself. For the case of the current behavior for `base`, `base` itself is not extracted. Because `parent` is relatively newer core module than `base`, `parent` itself is also extracted in this code though `base` is still not extracted. It might be considered as inconsistency.