* Removes sub-class constants definition from `Faraday::Error`. A sub-class (e.g. `ClientError`) was previously accessible
either through the `Faraday` module (e.g. `Faraday::ClientError`) or through the `Faraday::Error` class (e.g. `Faraday::Error::ClientError`).
The latter is no longer available and the former should be used instead, so check your `rescue`s.
* Introduces a new `Faraday::ServerError` (5xx status codes) alongside the existing `Faraday::ClientError` (4xx status codes).
Please note `Faraday::ClientError` was previously used for both.
* Introduces new Errors that describe the most common REST status codes:
* Faraday::BadRequestError (400)
* Faraday::UnauthorizedError (401)
* Faraday::ForbiddenError (403)
* Faraday::ProxyAuthError (407). Please note this raised a `Faraday::ConnectionFailed` before.
* Faraday::UnprocessableEntityError (422)
