Update README
Remove unneeded gems from Gemfile
Add license and update dependencies in gemspec
Simplify Rakefile
Ensure compatibility with Guard >= 2

Note: Guard initializes all plugins, even the ones that won't
be started so it's important to do any heavy work in the
#start method instead of in .initialize.
Bump to 1.0.0
Use run_on_modifications instead of run_on_changes
Update .travis.yml and gemspec
Merge pull request #20 from guard/v1

v1: compatibility with Guard 2 and improvements