the same values as open().

add private method to enum to support replacing global constants with Enum members:
- search for candidate constants via supplied filter
- create new enum class and members
- insert enum class and replace constants with members via supplied module name
- replace __reduce_ex__ with function that returns member name, so previous Python versions can unpickle
modify IntEnum classes to use new method

add private method to enum to support replacing global constants with Enum members:
- search for candidate constants via supplied filter
- create new enum class and members
- insert enum class and replace constants with members via supplied module name
- replace __reduce_ex__ with function that returns member name, so previous Python versions can unpickle
modify IntEnum classes to use new method