Move deprecation stuff into Guard::Deprecator
Move setup stuff into a new Guard::Setuper module
New `Guard::PluginUtil` class.
Deprecate Guard::Guard and replace it with Guard::Plugin
New Guard::Plugin::Base module common to Guard::Guard (deprecated) & Guard::Plugin
Rename Guard::Hook to Guard::Plugin::Hooker
Move Guardfile-related constants to Guard::Guardfile
Simplify Guard.within_preserved_state
Improve Guard.groups and Guard::Group#to_s
Misc minor code changes
Improve Guardfile
Remove Guard.quit? since it doesn't seem to be used!
New #title method for Guard::Group & Guard::Plugin