Warnings emited when building

[john-parton]

On master, cargo build emits 237 warnings.

Here are the different kinds of warnings:

• warning: trait objects without an explicit dyn are deprecated
• ... range patterns are deprecated
• unreachable pattern (this one has to do with the fact that Rust wasn't able to tell when a match pattern was exhaustive if you used all of the scalar values for a type, but now it appears to handle that correctly)
• use of deprecated item 'try': use the ? operator instead

You can run cargo build -v 2>&1 | grep warning | sort | uniq to get a summary.