Implement create_attribute() function

[luksak]

We should provide a way to use the create_attribute() function and provide an shim to a Attribute object of Drupal.

[luksak]

Ohhh... Look what I found: https://github.com/ericmorand/drupal-attribute
This should be fairly easy to implement. I'll try later today.

[luksak]

Basic support is working: #13

[yobottehg]

thanks @luksak we'll have a look

[luksak]

#13 adds very basic supprt. We should create a few issues against drupal-attribute. for example passing an argument to create_attribute() doesn't work currently.