Proposed fix for #1280

This PR proposes a fix for #1280, and #1676.

It is not ready to be merged, as I need a few more tests. 

Input for tests are very welcome.
The trouble seems to be that System.Uri never allows the use of escaped frward slashes. They are always translated into an actual path separator. So the path /containers/123/artist/AC%252FDC will always be split into the segment array shown in the image above. This is split way before we even start turning it into a Nancy.Url. 

So removing the trailing forward slash from the System.Uri segments won't really solve the issue reported.

We could of course just look at the original request url, and then just interpret it the way we want to. But I don't know what the standards are here. Is this simply not allowed, or is the System.Uri implementation just buggy.