Restructure to class-based Capistrano plugin

[ain]

Remove all inline methods in favour of the actual class that can be tested.

[ain]

Somewhere in Cap 3.5 code is plugin.rb that has rdoc docu connected to it.

The structure should be along the lines of

on roles(whatever) do |host|
    MyPlugin.dosomething(binding, host)
end

Also, sshkit allows contextual execution that can be used, e.g.:

context.execute :foo, :Bar, :Baz