Support rewrites separately from redirects

[mrled]

Currently we can do a browser redirect for /test to /somewhere/else/longfilename.pdf.exe.jpg.123 or whatever.

We could also support a rewrite - serve that asset directly from the /test path, without a redirect.

If someone has a use case for this, I would be interested in hearing it.

[mrled]

One idea for this use case is serving different content to different requests. I read https://justinjackson.ca/xslt and it occurred to me that you could serve a web page to browsers but an XML RSS document to podcast clients and feed readers.