Remove 'URIReference' from public interfaces

[lovelydinosaur]

Drops rfc3986.uri.URIReference from being referenced in any public interface.
In fact it wasn't actually included in URLTypes in the first place.

Our copy_with and join will be less efficient - but if we want to resolve that we should do it in a different way, rather than exposing implementation-level types in our public interface.

[lovelydinosaur]

We might also want to rethink the components attribute here - that's leaking implementation details at the moment.

A tighter API here would be for components to instead be _uri_reference.

We could also still expose a components interface, but as a plain named-tuple. (Or even a plain tuple, since we've got the by-name access anyway, and keeping a lower Type-surface would be good.)

[lovelydinosaur]

Right, I've also dropped the url.components interface here. We don't need it as a public interface, since we've got by-name access anyways. If we did want to expose a tuple-like interface too, than let's do that as a plain tuple, rather than exposing rfc3986 as part of our interface.

Let's keep a really tight API surface area wherever possible.

[sethmlarson]

Yep, this is what I was thinking for this as well.