add support for ratios

Getting the following stack trace. Might be related to this...

```
 Error: Invalid value for <path> attribute d="V25"raphael-min-2.1.2.js?body=1:10 qraphael-min-2.1.2.js?body=1:10 wraphael-min-2.1.2.js?body=1:11 c._engine.pathraphael-min-2.1.2.js?body=1:10 v.pathmorris.min-0.5.js?body=1:7 b.Grid.d.drawEventmorris.min-0.5.js?body=1:7 b.Grid.d.drawEventsmorris.min-0.5.js?body=1:7 b.Grid.d.redrawmorris.min-0.5.js?body=1:7 b.Grid.d.setDatamorris.min-0.5.js?body=1:7 dmorris.min-0.5.js?body=1:7 cmorris.min-0.5.js?body=1:7 cgraph.js?body=1:88 SubGraph.drawgraph.js?body=1:158 _results.push.$.ajax.successjquery.js?body=1:975 firejquery.js?body=1:1085 self.fireWithjquery.js?body=1:7804 donejquery.js?body=1:8519 callback
```