Added spec/dummy_app

This allows simple (manual) testing
More explicit path to the Notifier class.

Was failing to start in spec/dummy_app
Improved start/stop management

- Detecting if the start fails (10 seconds timeout). So Guard will be able to restart the app when files are changed.
- Improving stopping. Uses an INT signal instead of TERM, better with WEBRick.
Updated README
Bump to v0.0.6
Merge branch 'master' of github.com:rchampourlier/guard-shotgun
Updated gemspec
Updated Gemfile

- Added Jeweler
- Added RSpec (not used yet)