Change errors to error-chain or failure

[brandur]

Move the error system over to error-chain as it's starting to become a de facto standard in Rust and provides better introspection and some nice ergonomic improvements for projects using it.

[gsquire]

Another good candidate could be failure just FYI.

[brandur]

Another good candidate could be failure just FYI.

@gsquire Yep, good point. I don't have a strong preference, but if at all possible would like it'll be longest-lived and best-maintained. That might be either of them, but just given that it's a relatively new project, I might give failure a little more time to make sure that it makes it through its phase of adolescence.