Travis only for 1.9+
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
Fix changelog

[ci skip]
Update gem homepage (http://guardgem.org)

#427
Restructure README.

This moves some information to the wiki and changes some headings
to `h4`, so they won't appear on the guardgem.org menu.

The idea is to make the menu on the Guard homepage more slim and
focus on the important parts. Advances and rarely used stuff needs to
go to the wiki.
Fixes #453
Bump to 1.8.1
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