Bug 1232 - Add snippet of yang file into comments

- reworked all proposals from Tom Pantelis
- tested with toaster.yang, generated javadoc files added
  as attachment into bugzilla

Change-Id: I6a6c8a6f6592b1abf9368e9b8232263a029460a8
Signed-off-by: Ladislav Borak <lborak@cisco.com>