Correctly support `>=` and `<=` for type checking

When using mypy, > and < comparison is considered valid:

from ordered_enum import OrderedEnum


class TestEnum(OrderedEnum):
   ONE = 1
   TWO = 2
   THREE = 3

if TestEnum.THREE > TestEnum.TWO:
    pass

Success: no issues found in 1 source file

But if I use >= or <=, even though it works correctly, mypy reports an error:

from ordered_enum import OrderedEnum


class TestEnum(OrderedEnum):
   ONE = 1
   TWO = 2
   THREE = 3

if TestEnum.THREE >= TestEnum.TWO:
    pass

test.py:10: error: Unsupported left operand type for >= ("TestEnum")  [operator]
Found 1 error in 1 file (checked 1 source file)

Reproduce the issue with the two Python examples and mypy, comparing the existing behavior for > and < with >= and <=. Inspect the OrderedEnum implementation and its type-checking behavior; done means mypy accepts both inclusive comparisons while the runtime comparisons continue to work.