* Add some context to exceptions on unserializable
values (addresses #89).
* Document need to format merge data
(into something JSON-serializable).
* Add RemovedInDjrill2 DeprecationWarning.
* Deprecate blanket date/datetime serialization.
(Improves testing accuracy around API response encoding.)
* Add `six` as test dependency (six.BytesIO, six.b)
* Change MockResponse content to bytes (because HTTP responses
are bytes, not strings)
Second attempt to address possible test sequencing issue around tests that alter settings. (Failures in Travis tests not reproducible locally.)
Back-ports override_settings from Django 1.4 for compatibility with Django 1.3.
Treat image attachments with a Content-ID header as embedded, rather than ordinary attachments. (Rationale is that you must set the content-id to be able to refer to the image within your html, so that's a reasonable indicator to handle it as embedded.)
Introduce djrill.NotSupportedByMandrillError for unsupported functionality (previously used generic ValueError).
Change to djrill.MandrillAPIError, derived from requests.HTTPError, for API error responses (previously used djrill.mail.backends.djrill.DjrillBackendHTTPError -- retained as equivalent for backwards compatibility).
Add DjrillBackendMockAPITestCase.assert_mandrill_called; use it in representative backend test cases.
(Also make get_api_call_data work with various ways of calling requests.post.)
