Add OPML import.
Automatically save on elfeed-add-feed too.
Add OPML export.
Oops, autoload that one, too.
Remove hooks before running tests.
Use consistent random numbers for all test runs.

Conflicts:
	elfeed-db-tests.el
Drop multibyte<->unibyte stuff in elfeed-(un)ref.

Consistently encode content with UTF-8 in the content database
regardless of any configuration.
Enable more stringent content database tests.
Only hook emacs-kill-hook when interactive.