Gtfstk

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- Assembled ``feed.py`` and ``utils.py`` into a unified top-level package by tweaking ``__init__.py``.
- Renamed ``get_linestring_by_shape`` and ``get_point_by_stop`` to ``get_geometry_by_shape`` and ``get_geometry_by_stop``, respectively.

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- Added ``min_transfer_time`` to ``INT_COLUMNS``.

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- Fixed ``get_route_timetable`` sort order.

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- Added data frame empty checks to ``Feed.__init__``, because i was getting errors on feeds with empty ``calendar.txt`` files.

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- Removed ``parent_station`` from ``INT_COLUMNS``, which should have never been there in the first place.

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- Now you can specify the output distance units.