Document hook_features_disable_feature() and hook_features_enable_feature().

Bump, just spent hours trying to figure out why OG won't install its roles or permissions.
Turns out it is because it doesn't implement this hook.

If this were documented from the start, I wouldn't have had to dive into Features' code for about 5 hours only to discover there are two undocumented, yet important hooks.

Confirmed that still an issue, hook exists but documentation doesn't. Note this is a per component hook, not something anyone can implement

Don't think that is what caused the og issue; I think I recall seeing that in Og queue.

Seems like a good place for somebody to contribute a simple patch for easy commit credit ;) But this is in no way "Major"

Here is a patch.
Perhaps a lot more could be written about these hooks,
I think this is "better than nothing" and "good enough", considering how D7 near its EOL.