Updates for recent versions of Rust.

[simlay]

Hi friend,

I came across your project today and found it neat so I cloned the repo and messed around with it. Here's some of the updates I found to make clippy and the recent stable version of rust happy.

Here's the brief summary of changes:

• Added lots of dyns as suggested by clippy.
• Removed rust-toolchain because stable rust compiles the project.
• Fixed Doc-tests with ignore keyword (this simply doesn't test the snippet) but still produces the actual documentation.

There's still a bunch of unused code warnings but I figure this is still a WIP so I didn't touch those.

The reason there's so many changes is because I removed (most) unused whitespace. If you're unhappy with that, I'm okay with reverting that.

Also, I notice that the contributing guidelines mention running cargo fmt --all. I ran this after my changes and it resulted in 1423 deletions and 2139 additions.

Let me know if there's anything you'd like me to change.

Thanks,