continuation-based workflows

[earldouglas]

After reading the scala-user thread below, I took a stab at adding continuation-based workflows into Xitrum using code from the imperatively project.

This pull request includes the groundwork for writing Actions which include multi-step workflows written in an imperative style. I will submit a separate pull request to xitrum-quickstart with two example Actions.

scala-user thread: http://groups.google.com/group/scala-user/browse_thread/thread/cbb25bd3c88ff675
imperatively: https://github.com/JamesEarlDouglas/imperatively

[ngocdaothanh]

Thanks for contributing.

I've just added a sample for Knockout.js (please use the latest Xitrum source code):
https://github.com/ngocdaothanh/xitrum-quickstart/blob/master/src/main/scala/quickstart/action/TodoAction.scala

I think Knockout.js is perfect for continuation. They can come hand-in-hand together. With them app developers don't have to mess with request params, they only have to pass Scala case class objects from step to step in a typesafe way.

The only downside of Knockout.js is SEO because templating is done on the browser side.

[earldouglas]

Thanks for pulling my changes.

The Knockout.js example looks interesting. I will play with it and see if I can simplify it with continuations.