Bug fix in find_antiscion()

Was assuming that first parameter is a pointer to an enum. It is
actually an int converted to a pointer with GINT_TO_POINTER.
Fixed licensing issue

Fixes #2
Now using enum values instead of numbers in gswe_calculate_data_by_position()

It's just more beautiful.
Made HOUSE_SYSTEM_NONE a valid and working house system

Solves #1
Added some comments, mostly TODO items