Depth First Search

Initial version of the DFS algorithm has been added.
Currently 2 of 3 tests are failed.
Working on that.
Templates for two tasks + 1 additional task solved

Solution for task 'Tree height measurements' has been added
Template for task 'Azimuth at Treasure Island' has been added
Additional solution for 'Depth First Search' has been added.
Waiting for answer from task's owner about correctness of validation for
'DFS' task
(http://www.codeabbey.com/index/forum_topic/824fad27a7ac350fe93801fbf830a73d)