move "content" from attrs hash to separate arg, make it array aware

I would suggest to move content from args hash to third argument of el.create because current syntax do not allows creating such thing:
```html
<div content="some attr">some content</div>
```
and after change you could do 
```javascript
el.create('div', {content:"some attr"}, "some content");
```
or even allow content to be array:
```javascript
el.create(
 "ul", 
 {"content": "some attr"}, 
 [el.create("li", null, "first"), el.create("li", null, "second")]
);
```
to make
```html
<ul content="some attr">
 <li>first</li>
 <li>second</li>
</ul>
```