Return a 500 bad tracking # error

404 tells wombat the webhook url doesn't exist instead
Hard code all custom errors to a 500 response

Anything other than that might not be clear to Wombat that the request
did arrive at endpoint (but didnt go through all the way well)
Pass auth hash on sinatra specs
Use wombat_id instead of generic id for mapping
Prefix phone numbers with +
drop .ruby-version
Return friendly message when missing tracking number
Set aftership tracking status on shipment.status
Add placeholders for /get_trackings filters
Add regular gems for production
wombat readme