Add active method to session, retrieving active element
Add doc for active method in session
Add active test for active method in session
Fix unit test for active method
Update documentation
Add active session-command class
Use active session-command and re-use response-value method for active element
Remove available since comment
Add active session-command to Autoload
Merge pull request #25 from marcelerz/add_active

Add active method to determine active element