option to skip automatic injection of CSS into the DOM

I need CSS in the iframe - this is roughly equivalent to https://github.com/davidguttman/cssify/issues/7
can we change this to something slightly more terse? say
```javascript
var options = opts || {}
    , autoInject  = typeof options.autoInject !== 'undefined';
```

also, if we could stick to camelCase for the option keys that would be awesome. everything else looks good :)