Conference-scheduler

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* Bug Fix: Remove use of strings instead of datetimes for Slot.starts_at
`104 <https://github.com/PyconUK/ConferenceScheduler/pull/104>`_

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* New Feature: Equity objective function
`103 <https://github.com/PyconUK/ConferenceScheduler/pull/103>`_

* Incompatibility: New definition of tag based constraints
`102 <https://github.com/PyconUK/ConferenceScheduler/pull/102>`_

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* Bug Fix: Remove a circular import between scheduler and validator
`100 <https://github.com/PyconUK/ConferenceScheduler/pull/100>`_

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* Bug Fixes: Heuristic algorithmss
`98 <https://github.com/PyconUK/ConferenceScheduler/pull/98>`_
`99 <https://github.com/PyconUK/ConferenceScheduler/pull/99>`_

v.2.1.1 (2017-08-08)
--------------------
* Enhancement: ``scheduler.heuristic`` now returns in solution form
`97 <https://github.com/PyconUK/ConferenceScheduler/pull/97>`_

-------------------
* New Feature: ``scheduler.heuristic`` uses a heuristic method rather than an
integer linear programming approach

* Enhancement: ``scheduler.array``, ``scheduler.schedule_to_array`` and
``scheduler.solution_to_array`` now return arrays of integers, not
arrays of floats.
`94 <https://github.com/PyconUK/ConferenceScheduler/pull/94>`_

-------------------
* Incompatibility: ``Event.tags`` and ``Event.unavailability`` are now immutable
rather than list objects. List methods to update them will no longer work.

* New Feature: Methods to add tags and unavailability to Event objects
`77 <https://github.com/PyconUK/ConferenceScheduler/pull/77>`_

* Enhancement: the ``tags`` and ``availability`` arguments to ``Event`` are
optional, and default to an empty list.
`74 <https://github.com/PyconUK/ConferenceScheduler/pull/74>`_