Timecode

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* **Fix:** Fixed ``Timecode.parse_timecode`` for int inputs.
* **Update:** ``Timecode`` now accepts a ``fractional`` bool argument that
forces the timecode to be fractional.
* **Update:** ``Timecode`` now accepts a force_non_drop_frame`` argument
that forces the timecode to be non-drop frame.

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* **Update:** Added support for 23.976 fps which is a common variation of 23.98.

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* **NEW:** Support for passing a tuple with numerator and denominator when
passing rational framerate.

* **NEW:** set_fractional method for setting whether or not to represent a
timecode as fractional seconds.

* **Update:** Updated README's with info on new features

* **FIX:** Some merge issues.

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* **New:** Support for passing "binary coded decimal" (BCD) integer to
timecode argument as it's stored in certain formats like OpenEXR and DPX.
Useful for parsing timecode from metadata through OpenImageIO for instance.
Example: ``Timecode(24, 421729315) -> 19:23:14:23``
https://en.wikipedia.org/wiki/SMPTE_timecode

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* **Update:** To prevent confusion, passing 0 for ``start_seconds`` argument
will raise a ValueError now in ``Timecode.__init__`` method.

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* **New:** Added support for passing rational frame rate. 24000/1001 for 23.97
etc.

* **New:** Added tests for new functionality. Fractional seconds and
rational frame rates.

* **New:** added __ge__ and __le__ methods for better comparison between two
timecodes.

* **New:** Added support for fractional seconds in the frame field as used in
ffmpeg's duration for instance.

* **Important:** When passing fractional second style timecode, the
Timecode.frs will return a float representing the fraction of a second. This
is a major change for people expecting int values