Allow rendering of simple data passed to render

Since Padrino allows rendring of hashes and array 
````Ruby
render { :a => 1, :b => 2, :c => 3 } # => return a json string
````

I found myself doing:
````Ruby
render(@post && @post.attributes)
````

this leads to a 
````
undefined method `to_sym' for nil:NilClass
````

In the PR I have the rendering of some simple types e.g.

````
true, false, nil, 90
````

The PR would allow idioms like:
````Ruby
render(@post && @post.attributes)
render((true && false) && @post.attributes)
````