changelog: Add entry about better database performance

[ci skip]
url: Add parse_url_or_log()
engine,hook,process.web: Use parse_url_or_log().
engine: Poison workers if producer dies to avoid deadlock.
database: Add wrap.URLTableHookWrapper.
Move DB get/add/queued/dequeued hook concerns to URLTableHookWrapper.

queued/dequeued hooks get called for all add and check outs

Closes chfoo/wpull#190