Fix issue #1120

[narinluangrath]

• Add getPath prop to victory bar
• Add stories to storybook demonstrating usage
• For non-polar charts, getPath expects a function ({ x0, x1, y0, y1}) -> (string describing svg path)
• For polar charts, getPath expects a function ({ datum, start, end, r1, r2 }) -> (string describing svg path), where datum is an object of shape {x, y}, start/end are angles derived from styles.width, and r1/r2 are the radii (top/bottom) of each polar bar

[boygirl]

I would much prefer getPath to take a single argument props and have the same signature for polar and standard bars. To make it easier for folks, the props that we pass in can include all the pre-calculated values like width, startAngle and endAngle

[narinluangrath]

Yeah I was definitely not sure about what variables to include in the getPath function. Happy to make that change! Just to clarify, when you say the getPath function takes an argument props, you are specifically referring to this.props in the <Bar> component? You're not using props as a generic variable name?

I've changed the code so that getPath for non-polar bar charts has signature props -> svgPathString where props is a copy of this.props with additional fields x0, x1, y0, y1. The same is true for polar charts, except the additional fields are startAngle, endAngle, r1, r2.

FYI: I've added some stories to test the getPath prop but I'm really bad/slow at drawing svgs. Feel free to replace/remove that code.

[boygirl]

Yes! This is much better! Good to merge :)

[boygirl]

Also, your polar shooting stars look rad