url-authentication

- When credentials are included in a URL they are extracted and passed
  to the server using HTTP Basic Auth.

I've tested this by hand and it works.  I'm not quite sure how I
should test this in `test_requests.py`.  I would normally mock this
kind of thing, since I don't have a persistent service that requires
credentials running to use from a test, which seems to be the existing
pattern.  I'm reluctant to add a dependency on a mocking library and
jump through all those hoops if that technique is not already used.