Rotation support

[rshadow]

Hey. I use this in my project. But one day I needed to mark not only the waypoints but also the direction.

I added an implementation of the rotation of the marker for the triangle. But did not do for other types of markers. And I do not do a pull request. Because I'm not sure about the style of writing a module.

Have a look, please.

leaflet-svg-shape-markers.zip