title: Create additional D3.js symbols
body: <p>D3 already features a bunch of <a href="https://github.com/mbostock/d3/wiki/SVG-Shapes#wiki-symbol" rel="noreferrer">symbols</a>, but I'd like to add a custom one. So that I could for example just call <code>d3.svg.symbol().type('custom')</code> in my code.</p>