Moved and updated criterion into dev-dependencies

[ivanitskiy]

this would sove the issue when running cargo bench, as the criterion is a dependency, but it seems to me and the criterion docs it should be used in dev-dependencies section of Cargo.toml file.

[ivanitskiy]

I also find that the examples folder should use also serde, and bincode are candidates to be moved to the dev-dependencies section. so instead of cargo run --example bench --features=serde,bincode people can run just simply cargo run --example bench. happy to commit this change too if no objections

[spacejam]

thanks! and that's a good point wrt serde and bincode as dev deps, I'll add that now