Fix loading of gem via Bundler :path

Because of the collision between the Guard::Yard module and
Guard::Yard class, there was a problem loading the guard-yard plugin
via :path using Bundler. This change, based on the method the
guard-rspec plugin uses, corrects that problem.
Add NullObject server
Merge pull request #9 from lee-dohm/master

Add the ability to not start a server, just update the documentation