release/repo file - more stuff

I'm not sure how useful this is for apt-deb b/c I'm not sure how debs
handle gpg signatures.

But would it be useful to add, to the common metadata, an optional
location for a gpg public key that the packages are signed with.

<repository>
  <name>..</name>
  <key type="gpg" url="http://complete-url"/>
  ...
</repository>

maybe let that be listed multiple times for multiple keys...

thoughts, should this be in a namespace or would it be useful for
debian/apt as well?

-sv