added TestCase
change headers default value
change decode method
edit test
add headers dlm bentuk dictionary
parameter headers sebelom priority
Changed the field into JSONField
Refactored the logic to add headers
Make headers not required by default, default to None
Not hard require django jsonfield
Merge pull request #15 from wadevries/master

Fixes https://github.com/ui/django-post_office/issues/14 . Thanks @wadevries
Backend now checks for HTML alternative and properly persist it into DB. Fixes #16.
Merge branch 'master' of github.com:ui/django-post_office
Merge branch 'jessica-master' of git://github.com/SeiryuZ/django-post_office

Conflicts:
	post_office/mail.py
	post_office/tests/models.py
Updated README.rst.
Fixed Travis build.
Added deprecation warning to send_mail and send_templated_mail commands.
Updated README.
Email sending can now be scheduled.
Updated README.