Accept &str for Redirect

[emschwartz]

Motivation

http::Uri strips URL fragments, which are important for redirects, for example for login flows with access tokens in the fragment.

Solution

As discussed in #888, this changes the Redirect struct to accept a &str instead of a Uri.

Resolves #888

[jplatte]

CI fails because you didn't update the example in the docs for the Redirect type.

[davidpdrsn]

Thanks!