Added ability to add args to callbacks `after` and `before`.

Commet from @michamilz: http://www.jetthoughts.com/tech/2013/09/26/capistrano-3-passing-parameters-to-your-task.html#comment-1233054544

Added ability to provide args to callbacks. Example we have task with args:

```ruby
desc 'Example of task with args'
task :uname, :opt do |task, args|
  on roles(:app) do
    execute :uname, args[:opt]
  end
end
```

To provide args for callbacks in current version:
```ruby
before :started, "uname_a" do
  Rake::Task[:uname].invoke('-a')
end
```

Added a new implementation:

```ruby
before :started, :uname, '-a'
```