Feature/has many

Can you review this change and see if it makes more sense?

Mostly it's POD changes, but I've also fixed what the DBRef holds in the database. Previously the '$ref' part did not hold the correct value. This is back compat, since the code only query the '$id' part, so I'm not sure if we need to warn about it.

Please hit the "Merge" button if you like the changes @jberger.