Add SubSlice to return slice of sub vipers

[andig]

Replace #509. Fixes #171, #504, #800.

[CLAassistant]

All committers have signed the CLA.

[andig]

@sagikazarmark I realize there is a big number of open PRs. Is this one you'd consider given it addresses a number of open issues?

[andig]

ping gentle nudge @sagikazarmark any chance to get your review?

[andig]

I'm also watching #866. In case that gets merged I'll check if it makes sense to carry the flag assignment over.

[sagikazarmark]

Sorry @andig , my hands are full right now. I'll take a look at your PR when I get the chance,

[criscola]

I would be interested in having this...

[ben-turner]

I usually try to avoid "bump" and "+1" comments, but this seems like a fairly straight-forward PR that provides a lot of value, so I just wanted to bump it up to the top of the list before it gets lost to time.

[andig]

Fixed the merge conflict while we're approaching 6th birthday of this PR. I can't even remember why I've added this. Is there still demand? Otherwise I'd like to close here ;)

[andig]

Actually, all issues have been closed as "not planned". Closing here. Sorry for the noise.