Adding support for basic auth in webhook URLs

which takes precedence over the custom Authorization header made from the SHA256 hash of the repo slug + token.

This parsing is automatic when the Faraday builder is constructed with a `url` arg or a `Faraday::Connection` is initialized directly with a `:url` arg.  Since the Faraday builder is cached in `@http`, it looks like we instead have to parse and unescape the basic auth params directly.  If a more invasive redesign is desirable that takes advantage of Faraday's built-in basic auth support, I'll gladly do that instead :smile_cat: