Improve Guard.groups and Guard::Group#to_s
Remove Guard.quit? since it doesn't seem to be used!
New #title method for Guard::Group & Guard::Plugin

Also, streamline requires
Improve Guard::Dsl API and documentation
Re-add .template in Guard::Plugin::Base

We don't need to break the current API too much! :)

Also, more documentation for Plugin::Base, Setuper and Group
Refactor and document Guard#guards, Guard#groups, Guard#add_guard and Guard#add_group
Move Guardfile evaluation stuff into Guard::Guardfile::Evaluator
Deprecate Guard::Guardfile in favor of Guard::Guardfile::Generator

Also, refactor Guard::DslDescriber, re-add Guard's deprecated
methods (now in Guard::PluginUtil) and allow
Guard::PluginUtil#initialize to take 'guard-xxx' or 'xxx' as argument
Move colors from Guard::UI to Guard::UI::Colors
Deprecate Dsl & DslDescriber properly
Improve gemspec, .gitignore, .travis.yml and checked Yardoc
Move deprecated methods into a new Guard::DeprecatedMethods module
Deprecate Guard.guards in favor of Guard.plugins
Deprecate Guard.add_guard in favor of Guard.add_plugin
Move Guard main commands (start, stop, reload, run_all, pause…) to a new Guard::Commander module
Improve interactor code and specs
Improve overall documentation consistency and README
Improve notifiers code
Refactor notifiers

Notifiers are now classes with a common interface
inherited from `Guard::Notifier::Base`:

* `#notify` (required)
* `.available?` (optional)
* `.supported_hosts` (optional)
* `.gem_name` (optional)

Introduce a new `#normalize_standard_options!` method to
avoid having a weird implementation for `#notify` in
Guard::Notifier::Base!