Consider removing failure crate

[jgrund]

Consider removing the failure crate and replace with implementation for std::error::Error and conversions.

[xoac]

There are crates like thiserror that makes implementation of std::error::Error supper easy

[Empty2k12]

I'm all in favor of removing dependencies. Feel free to open a pull request!

[qm3ster]

It would not be "removing a dependency" in the strictest sense, but thiserror derives errors that are indistinguishable from manual implementation of std::error::Error trait, and so will not pollute users.