Tracker: rand_core 0.6

[dhardy]

A new release is expected to:

• fix Fix next_u64_via_fill to use little endian order #1026 (endianness for next_u**_via_fill)
• update to support getrandom v0.2 when released

Any new release also fixes:

• Enable documentation of os module (docs.rs fails to load #1001)

[newpavlov]

Also test performance of bit-level counter for BlockRng.

• Add RngCore::next_bool: Add next_bool method to RngCore and counter levels to BlockRng #1031

[dhardy]

I think there are no more blockers to this release?

Since #1031 has not reached a conclusion it may be better to leave this be for now (although possibly other parts of that PR could be merged without the bit-level counter).

[dhardy]

This is done.

Do we add a compatibility shim? Last time we didn't (#819). This time it's probably easier, but IMO not the right approach. If we do, I'd prefer to make it opt-in (i.e. someone would have to depend on rand_core = { version = "0.5", features = ["shim"] }).

Anyway, we can close this tracker.