add a path filter t the AtomStream:
- the AtomInject plugin receives a PUT request on a given path ("$put_path") with the content of an entry.
- the AtomStream plugin receives a GET request on another path ("$get_path/atom-stream.xml") (the arg 'since' is still allowed)
$put_path and $get_path can be '/' or '/a' or '/a/b', ....
then the AtomStream plugin produces a result filtered like this:
GET /atom-stream.xml returns everything ('/' or '/a' or '/a/b')
GET /a/atom-stream.xml returns the entries put with '/a' or '/a/b'
GET /a/b/atom-stream.xml returns the entries put with '/a/b'