Typed Tutorial

As part of learning Scalding, I wrote a new version of the tutorials that uses the Typed API, and I thought I would share it here in case it could be helpful to people learning Scalding for the first time, so they have some more examples walking through how the Typed API works.

If you have feedback on style, idioms, or my descriptions are incorrect or unclear, I would love to hear it so I can fix it, and more importantly, learn how scalding works.

I also made this all one file, with the different tutorials selected using a command-line flag because I found it easier to see everything in one file. But I would be happy to break it out into separate files as the original tutorial did.
Hmm, yes it is messy. I found it useful to see the types in order to understand how various tuples end up nesting when you group and join. For instance here, I wanted to note that join takes you from `[String,Long] join [String,Double] -> [String,(Long,Double)]`.

Could probably talk about those types transformations in comments without writing out the `CoGrouped`, etc.