Add json helper functions, and remove some old, dead code.
Remove all datacratic and rubicon extensions to the OpenRTB structs.
Add a class imitating C++11 non-static data member initializers.
Add new value descriptions.
Add automatic casting support.
Refactor the OpenRTB structures.
Fix AppNexus "support".
Temporary: drop dependency on https://github.com/datacratic/soa/pull/22.