This will allow us to like to specific snippets of code in the
documentation.  I plan to create a tutorial similar to the C# tutorial
https://developers.google.com/protocol-buffers/docs/csharptutorial

Since that tutorial has sections for populating a proto, parsing, and
serializing, I made a region for each of these for Go.  To make the
populating sample more self-contained, I refactor the listing example
slightly.