WIP parallelized email sending.
First seemingly working implementation of parallel sending.
Added a workaround for Travis multiprocessing issue.
Moved logic for getting emails to be sent to mail.get_queued().
Added -p or --processes option to send_queued_mail management command.
Updated README.
Merge branch 'master' of github.com:ui/django-post_office into parallel-send

Conflicts:
	README.rst