Add python 3 support

Add support for python 3. Retain support for python 2.7

Release support for Django 1.11

Switches the repo to use tox for testing, and runs tests with both 1.8 and 1.11.

Handle invalid relationship type gracefully

Returns an empty list instead of throwing an error when a user tries to get milestones of an invalid relationship type. Removes API-level validation of relationship types, though data-layer validation remains.

v0.1.9

Adds a XBlock runtime service, MilestonesService

release-2015-10-20

Version: 0.1.3
Date: 2015-10-20
Commit: 4088018
Notes: Adds find_packages() to setup.py in order to include all necessary packages/modules

release-2015-10-19

Version: 0.1.2
Date: 2015-10-19
Commit: fb6eaa7
Notes: Includes all changes added since 2015-06-17 (0.1.1)

Release 2015-06-17

Merge pull request #10 from edx/asadiqbal08/SOl-639

(WIP) SOL-639