ST3 support, "Specific files only" functionality, improved TODO list navigation

I put together all changes that have been made so far by most of the forks, so you can merge them and bump the SublimeTODO version. We will be happy to see the updated version of SublimeTODO that supports ST3 and many new features. Thank you!

CHANGELOG:
* ST3 Support;
* "Specific files only" search functionality;
* Read settings from user settings file;
* "XXX" pattern match;
* TODOs in file menu;
* SublimeTODO preferences;