Add example for rendering custom point symbols

examples/earthquake-custom-symbol.html

@@ -0,0 +1,9 @@
+---
+layout: example.html
+title: Earthquakes with custom symbols
+shortdesc: Demonstrates the use of `ol.render.toCanvas` to create custom icon symbols.
+docs: >
+  This example parses a KML file and renders the features as a vector layer.  The layer is given a <code>style</code> that renders earthquake locations with a custom lightning symbol and a size relative to their magnitude.
+tags: "KML, vector, style, canvas, symbol"
+---
+<div id="map" class="map"></div>