Merge pull request #12 from paulrayner/mongoid

Add mongoid notes.
Create failing specs for Delivery.
Start adding methods to Delivery. Tests not passing yet.
Get test passing naively.
Start adding logic to Delivery.
Fix up first Delivery spec. Add code for 2nd spec.
Get compiling.
Fix logic a little for Delivery.
Get 2nd Delivery spec passing.
3rd spec for Delivery.
Get final Delivery spec passing.
Extract method to create fake handling event.
Use fake handling event in all specs.
Get last known location tests passing.
Get last known location specs passing properly.
Get specs passing naively for misdirected Cargo.
Make new method in Delivery for misdirection status.
Start implementing is_misdirected for Delivery, which requires is_expected for Itinerary.
Get first is_expected spec to pass for Itinerary.
Isolate nasty search for leg unload location.