Upgrading to Guard 2.0

This is a WIP, please not edit. Thanks, @rymai.

Guard 2.0 comes with several API changes (the majority is backward-compatible, but not all).

Guard::Guard deprecated in favor of Guard::Plugin

To remove the confusion between Guard and its many plugins (guard-rspec, guard-pow, guard-livereload etc.), Guard::Guard is renamed Guard::Plugin. Guard::Guard is deprecated so if you're a plugin maintainer, in your next (major) release that will depend on Guard ~> 2.0 you must make your plugin inherit from Guard::Plugin instead of Guard::Guard.

Also, please be sure to change the #initialize signature from #initialize(watchers = [], options = {}) to #initialize(options = {}) (watchers are now passed in the options argument directly).

For instance, for guard-rspec:

module Guard
  class RSpec < Guard
    def initialize(watchers = [], options = {})
      super
      # rest of the implementation...
    end
  end
end

should become:

module Guard
  class Bundler < Plugin
    def initialize(options = {})
      super
      # you can still access the watchers with options[:watchers]
      # rest of the implementation...
    end
  end
end