Remove quick-error dependency?

[jplatte]

Since you removed it from humantime, maybe you're planning to remove / replace it here too? I hardly see it used anymore, and would be happy to have a slightly leaner dependency graph :)

EDIT: I had a look at quick-error again, it seems less heavy than e.g. failure or snafu. So I guess it's fine, though it could still be an improvement for readability to remove the dependency. Feel free to close this issue without further comment if you want to keep the dependency.

[tailhook]

Removing it in favor of manual code like in humantime can be done if contributed. The hardest part of that is keeping backwards compatibility with old error. I don't see any reason of replacing it with some codegen library at this moment as this is a pretty small and low-maintenance crate (i.e. new errors would not happen too often).