feed: Pass config and section arguments to get_message()

feed: Pass config and section arguments to get_message()

Otherwise it will always use the default config.

Also add section fallback code to get_message in case the
feed-specific section is not in the config file.  This is useful for
testing, although in production every feed should have a section to
hold it's URL.

Signed-off-by: W. Trevor King <wking@tremily.us>