Serhiy's patch is only for IntFlags, and my patch hasn't yet fully incorporated his (many thanks for decompose!)

For IntFlags I do not expect to have very many instances alive at once, especially since not-bitwise operators will lose the IntFlag class and become plain ints.

Flags are closed.  If the zero value is not specified the repr and str are:

>>> Hah(0)
<Hah: 0>
>>> str(Hah(0))
'Hah.0'

(An RGB class might be:  <RGB.Black: 0>)

A question I have about IntFlags:

If a third-party lib specifies that certain bits are reserved and should always be zero (or at least not changed), do we want to add some easy support for that?