Support multi line attribute assignment

• Add support for doc string and data table

Example:

Feature: Cucumber factory test feature

  Scenario: Some example
    Given there is a user with the role "admin" and these attributes:
      | first name       | Jane  |
      | last name        | Jenny |
      | offer permission | false |

  Scenario: Some example
    Given there is a user with the role "admin" and these attributes:
      """
      first name: Jane
      last name: Jenny
      offer permission: false
      """

See README.md for more details.