Major refactor of message attachment handling; no longer stores verbatim

message copy in database.

Bumping version number to 2.1

* Walks through incoming message, write attachments to disk as they are found,
  and alters message body removing actual attachment body, and adding
  header 'X-Django-Mailbox-Interpolate-Attachment' referencing the ID of the
  stored attachment.
* When calling ``get_email_object``, will walk through stored message, and
  're-hydrate' the message by finding said headers, searching for the
  appropriate record in the MessageAttachments table, and rebuild the message
  object as closely as possible.

Minor fixes:

* Properly collect text/plain content from any part of the message; previously
  would only check the message's first level of payloads, now walks through
  all payloads, building a string of all text/plain content.
* Remove use of deprecated `assertEquals` message.

setup.py

@@ -1,14 +1,17 @@
 from setuptools import setup
 
-tests_require=[
+tests_require = [
     'django',
 ]
 
 setup(
     name='django-mailbox',
-    version='2.0',
+    version='2.1',
     url='http://bitbucket.org/latestrevision/django-mailbox/',
-    description='Import mail from POP3, IMAP, local mailboxes or directly from Postfix or Exim4 into your Django application automatically.',
+    description=(
+        'Import mail from POP3, IMAP, local mailboxes or directly from '
+        'Postfix or Exim4 into your Django application automatically.'
+    ),
     author='Adam Coddington',
     author_email='me@adamcoddington.net',
     tests_require=tests_require,