Prepare package for Meteor 0.9

I've been using your package as part of a migration to Meteor 0.9 and so I've updated it to work with the new system.

Note that your package was migrated as `mrt:bootstrap-3` which you will probably want to re-publish as `mangasocial:bootstrap-3` or whatever name you want.

Also note that the `api.add_files` function doesn't work the same way for assets in 0.9 and as a result the CSS overrides and fonts in this package need to be verified as working properly. I am currently working on that as well and we can follow up in this thread.

There are still some kinks being worked out; see https://hackpad.com/Migrating-Packages-zN0we9sIjkH and https://meteor.hackpad.com/Unipackage-tvas8pXYMOW#:h=Publishing-a-New-Package.

Let me know if I can help with any issues. The big discussion thread is over at https://groups.google.com/forum/#!topic/meteor-talk/VUaWMwV7aHM.