Allow borderColor to be customized through border options

[pateketrueke]

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Description

Add a new border option to customize borderColor through, similar to color.

Testing

Now we're able to do this:

new Chart(ctx, {
  type: 'candlestick',
  data: {
    datasets: [{
      color: {
        up: 'rgba(52, 207, 51, 0.5)',
        down: 'rgba(173, 0, 44, 0.5)',
        unchanged: '#747f89',
      },
      border: {
        up: '#34CF33',
        down: '#AD002C',
        unchanged: '#747f89',
      },
      borderWidth: 1.5,
      // more options & data
    }],
  },
});

And colourfully we got this:

[benmccann]

Cool!

I would suggest we still use the borderColor attribute instead of having border and borderColor. We could check if it's a string or object. If it's a string we use it for up, down, and unchanged. If it's an object we use the corresponding attributes inside. We should support the same syntax for color as well for consistency

[pateketrueke]

Hi, I just applied the changes as you told me.

Thanks for your feedback! 🎉