Changinig gtags to work with Sublime Text 3
Modified README, to include steps for setup.
Modified gtagsplugin.py, to change import statements based on version, to make it compatible with ST3
Update README.md

Fixed formatting errors
Update gtagsplugin.py

Fixing Typo error
Merge pull request #13 from o-darshan/master

Changinig gtags to work with Sublime Text 3