Error patches

[yoshuawuyts]

This updates the Error and ErrorKind types to contain a StatusCode field that can be used to set a status code. This will help us make progress on:

• migrate from io::Error to http_types::{Error,ErrorKind} #41
• Use Error/ErrorKind from http-types async-h1#46
• Handling Errors in Route Handlers tide#138
• Implementing IntoResponse for tide::Result<tide::Response> tide#371 (comment)
• A re-work of the error handling system tide#389
• Convert Exception to Error. surf#113
• Convert Exception to Error cont. surf#133

Additionally we can now cast any Error + Send + Sync to an http_types::Error, with support for downcasting and traversing error chains.

Changes

• Polishes Error and ErrorKind
• Replaces all placeholder instances of io::Error with http_types::Error

Todos

• fix tests
• remove todo!s
• replace ParseError types
• add bail!, ensure! and format_err! macros

[dignifiedquire]

👌