Improved API docs

I think @adam-lynch was running and old version of the software when he reported [this issue](https://github.com/75lb/dmd/issues/6).. anyway, it works fine without his hack.. in general, before running grunt do an `npm update` in your working directory to ensure all the latest modules are in place.. 

You can see how the README will look with this patch [here](https://github.com/75lb/node-webkit-updater)

All i have done is inserted a `{{>main}}` partial into your README template, oh and i bumped the initial heading depth to 2 so it fits in better with your general doc outline.