Add a workaround to include conditional comments, and include html5shiv

By default, Go Templates remove HTML comments from output.

This has the unfortunate side effect of removing Internet Explorer conditional comments.

This commit adds a simple workaround suggested in the [hugo docs](http://gohugo.io/templates/go-templates/) and includes [html5shiv](https://github.com/aFarkas/html5shiv) for IE9- .

Thanks!