Behat/Drupal - Drupal Extension: use drupal and drush driver at the same time in different scenarios

Originally in drupal-extension you could use only one driver at time to perform the tests using the tag @api.
After my (merged) pull request you can use both and then benefit from the unique specifications of each driver.

Before:

Drupal\DrupalExtension\Extension:
    api_driver: "drupal"

Now:

Drupal\DrupalExtension\Extension:
    api_driver: "drupal"
    drush_driver: "drush"

Example with a feature:

@api
 Scenario: Scenario description that use drupal driver

@ drush
 Scenario: Scenario description that use drush driver

Tnx to my colleague @mavimo for the partecipation

Issue on drupal.org - https://drupal.org/node/2077861