Adds three new statements:

• Given the file :filename
• Given files:

Add the new Palantirnet\PalantirBehatExtension\Context\DrupalFileContext class to your behat.yml to use these, and then you can do a scenario like:

Scenario: Add a file.
  Given the file "foo.txt"
  And files:
    | filename | author   |
    | bar.png  | admin    |
    | test.pdf | somebody |

This is most useful when combined with the file field handler work I have here: https://github.com/becw/DrupalDriver/tree/file-field-handler (specifically, Driver/Fields/Drupal7/FileHandler.php)