Support both array and comma separated string as arguments

Hey Guys,

Don't you guys think this may be a good idea to support both array and comma separated string as arguments for dynamic query function? 

$selectArray = array('id', 'username', 'age');

...
->find(function($query) use ( $selectArray ){
         $query->select( $selectArray );
   }
...


In terms of aliases, I think it should be pretty clear to a user that aliases are only introduced in the scope of aggregations. And, if the passed array is something completely wild, it should be pretty clear to the user what they've done when it blows up in their face. I think any misconceptions of what these methods expect could be made clear in the README and in the future `gh-pages` to avoid any confusion. I'm :+1: on this PR, since it opens up building arrays of selected fields from a dynamic source... if that were ever to be a thing.