importfeeds: use bytestring paths
changelog note for #85
fix inline and rewrite for instance fields

I'm transitioning to using exclusively instance-level fields instead of
class-level fields in plugin objects, but I neglected to bring inline and
rewrite into the future. This manifested as silent inaction on the part of
these plugins.

This change restores the old behavior (for compatibility) but also updates the
plugins to use the new behavior.