Split JitterRng into a separate crate

[newpavlov]

#681

[dhardy]

Nice job but writing the impl before any decision is potentially a wasted effort. I appreciate the extra modularisation though.

Note if we do use this code: don't forget the copyright boilerplate this time (excepting the log shim which is trivial).

[vks]

I think rand/utils/ci/script.sh still needs to be updated to include the new crate.

Looks good, besides the nits!

[vks]

Looks good to me now, thanks! Let's make sure to resolve the discussion in #681 before merging.

[dhardy]

If we are going to do this, then I think it should be an optional dependency.

[newpavlov]

Then you'll have to publish v0.7, as JitterRng export is not feature gated right now.

[dhardy]

Summary from #681 and #699:

• there are some reservations about JitterRng's security (JitterRng security #699)
• we decided to stop using this as a direct dependency of Rand, though not to make breaking changes before 0.7 so this is still a dependency for now
• when no longer a dependency, this will migrate to a new repository