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.
should we also mention that this is the same as `sumByKey`?