Merge pull request #54 from austinwitherspoon/add-type-hints

Add type hints, and restrict package to 3.7+

- Bumped up version number.

- Updated readme to clarify the supported frame formats.

* **Fix:** Fixed 23.98, 29.97 DF, 29.97 NDF, 59.94 and 59.94 NDF roll…

…over to ``00:00:00:00`` after 24 hours.

* **Fix:** Fixed a huge bug in 29.97 NDF and 59.97 NDF calculations i…

…ntroduced

  in v1.2.3.

* **Fix:** Fixed ``Timecode.framerate`` when it is given as ``23.98``. The
  ``framerate`` attribute will not be forced to ``24`` and it will stay
  ``23.98``.

* **Update:** ``Timecode.tc_to_frames()`` method now accepts Timecode instances
  with possibly different frame rates then the instance itself.

* **Fix:** Fixed ``Timecode.div_frames()`` method.

* **Update:** Test coverage has been increased to 100% (yay!)

* **Fix:** Fixed ``Timecode.float`` property for drop frames.

* **Update:** It is now possible to supply a ``Fraction`` instances f…

…or the ``framerate`` argument.

1.2.3

=====
* **Update:** Passing ``frames=0`` will now raise a ValueError. This hopefully
  will clarify the usage of the TimeCode as a duration. If there is no
  duration, hence the ``frames=0``, meaning that the number of frames of the
  duration that this TimeCode represents is 0, which is meaningless.
* **Update:** Also added some validation for the ``frames`` property
  (oh yes it is a property now).

* **Update:** Version bump for PyPI.

* **Fix:** Fixed a test that was testing overloaded operators.