Write trait requirements in documentation.

I've not done any generated HTML in the past so please point out any formatting issues.
> ### DeadBuildingState
> Requires traits: `Health`, `RenderSimple`.
> <table>
> <tr><th>Property</th><th>Default Value</th><th>Type</th><th>Description</th></tr>
> <tr><td>LingerTime</td><td>20</td><td>Integer</td><td></td></tr>
> </table>

vs

> ### DeadBuildingState
> Requires traits: `Health`, `RenderSimple`.<br /><table>
> <tr><th>Property</th><th>Default Value</th><th>Type</th><th>Description</th></tr>
> <tr><td>LingerTime</td><td>20</td><td>Integer</td><td></td></tr>
> </table>