Allow for attribute

[emersion]

Allow to use for instead of htmlFor:

The new ECMAScript 5 specification allows property names to be reserved words.

http://stackoverflow.com/questions/4298594/javascript-keywords-in-hash-keys

[emersion]

Even if for is reserved (on old browsers), this works:

{ for: 'my-id' } // New browsers
{ 'for': 'my-id' } // Old browsers