Region#show return 'this'

Nested layouts:

    myRegion1.show(new MyLayout1());
    myRegion1.currentView.myRegion2.show(new MyLayout2());
    myRegion1.currentView.myRegion2.currentView.myRegion3.show(new MyLayout3());

can now be written as:

    myRegion1.show(new MyLayout1())
      .currentView.myRegion2.show(new MyLayout2())
      .currentview.myRegion3.show(new MyLayout3());
Merge branch 'patch-1' of github.com:aaronz8/backbone.marionette into patch-1