Chartify

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Improvements:

* Added second Y axis plotting.
* Removed Bokeh loading notification on import (Thanks canavandl!)
* Added support for custom Bokeh resource loading (Thanks canavandl!)
* Added example for Chart.save() method (Thanks david30907d!)

Bugfixes:

* Updated documentation for saving and showing svgs.
* Fixed bug that broke plots with no difference between min and max
points. (Thanks for finding fabioconcina!)

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Improvements:

* Updated docstrings (Thanks gregorybchris ItsPugle!)
* Added SVG output options to Chart.show() and Chart.save()
(Thanks for the suggestion jdmendoza!)

Bugfixes:

* Fixed bug that caused source label to overlap with xaxis labels.
* Fixed bug that prevented x axis orientation changes
with datetime axes (Thanks for finding simonwongwong!)
* Fixed bug that caused subtitle to disappear
with `outside_top` legend location (Thanks for finding simonwongwong!)
* Line segment callout properties will work
correctly. (Thanks gregorybchris!)

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* Updated Bokeh version requirements to support 1.0

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* Removed upper bound of Pillow dependency.

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* Stacked bar and area order now matches default vertical legend order.
* Added method for shifting color palettes.
* Added scatter plots with a single categorical axis.
* Fixed bug with text_stacked that occurred with multiple categorical levels.

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* Fix scatter plot bug that can occur due to nested data types.