Use the failure crate for error handling

[thomaseizinger]

https://boats.gitlab.io/failure/intro.html

This is a nice refactoring task that can hopefully be done incrementally. In a nutshell, it allows you to always use the same Error type as a return value (failure::Error) as long as all your custom errors implement failure::Fail. This should get rid of all your From implementations of the errors.

[LLFourn]

@thomaseizinger we kind of do this already. I'm still not 100% confident on when to use it but maybe this can be closed?

[D4nte]

Deprecated:

Heads up, failure crate users, especially library authors! The failure crate is starting to fall by the wayside, since std::error::Error is being fixed to provide the same benefits of failure::Fail, so its usage is being increasingly discouraged in the Rust ecosystem. See this issue for details: rust-lang/rust#53487