Even more fluent eloquent model via magic setters

Now it is possible to use Eloquent's magic setters in chains. For example:

    $model->set_foo('foo')->take(10)->set_bar(some_function());
    // ...even though setters 'foo' and 'bar' are not defined on the model
Return `$this` in `set_attribute`
Merge pull request #1976 from neoascetic/more_fluent_eloquent

Even more fluent eloquent model via magic setters