New stroke-linecap and stroke-linejoin style options with VML alternatives. For #1843.

Based on the following documentation:
- linecap: [SVG](https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/stroke-linecap) and [VML](http://bit.ly/15pnUFT)
- linejoin: [SVG](https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/stroke-linejoin) and [VML](http://bit.ly/15ppCqU)

 For #1843