First cut at reintroducing object serialization.

First cut at reintroducing object serialization.

This is very much based on the work t0m did in his json branch (which
was merged into swann to become swann-with-json). The nicely broken up
Git objects created more replicated code than I like but it seems to work
which is enough for now. Next up is the rest of the objects and then onto
a shiny new REST interface.