Tracking issue for next release series

[tarcieri]

This is a tracking issue for the next set of breaking releases which are currently under development on the master branch.

These are somewhat interdependent on RustCrypto/traits#1571 as noted below:

• block-buffer v0.11 (depends on crypto-common v0.3)
• block-padding v0.4 (depends on hybrid-array v0.3)
• dbl v0.4 (depends on hybrid-array v0.3)
• inout v0.2 (depends on block-padding v0.4)

[tarcieri]

@newpavlov I'm wondering if we can cut final releases of some or all of these now and start getting the ball rolling on stable releases

[newpavlov]

One potentially unresolved problem with block-buffer is efficient serialization of eager buffers (current version of digest serializes eager buffer into block size + 1 byte, while block size would be sufficient). Right now we have inherent serialization methods, but unfortunately they are a bit hard to combine with implementation of SerializableState. I will try to work on it during this weekend.

I also thought about moving buffer implementation used by the stream cipher wrapper to block-buffer, since it's the only place in cipher which uses unsafe.

Another change which I would like to introduce is a minor change to the blobby format as noted here.

Finally, regarding dbl, we probably should make a decision on #1077. It does not prevent us from cutting a release and deprecating it later, but I think it would be better to not cut a potentially quickly deprecated release.

Otherwise, I don't have objections to cutting the releases.