fixing deps inconsistencies and clippy errors

[sabify]

This PR will resolve cargo's install and clippy errors due to deps inconsistencies.

[Noah-Kennedy]

@jeff-hiner not sure how I feel about pre-release crates for cryptography, would like your comment on this.

[jeff-hiner]

We've been awaiting official releases of RustCrypto crates for several months now. The transitive deps on old rand_core are awful.

I do agree that it's preferable to not pin to .pre candidates, but in this case as a compromise I think we could reasonably cut a 0.5.0-pre release on our own side with these changes and pend a full release on RustCrypto stuff being updated.

Also we should try to apply some pressure to the RustCrypto maintainer to cut a release. The stated reason for not doing so earlier was because of rustc version requirements, but the version in question has been stable for a while, and that's exactly what minor rev bumps are for.

[sabify]

Any plan to merge this PR?

cargo install doesn't work at the current stage.

[Noah-Kennedy]

@jeff-hiner I'm going to defer to you here.