def purchase(email, items, incomplete = nil, message_id = nil, options = {})
      data = options
      data[:email] = email
      data[:items] = items

      if incomplete != nil
        data[:incomplete] = incomplete.to_i
      end

      if message_id != nil
        data[:message_id] = message_id
      end
      api_post(:purchase, data)
    end
def purchase(email, items, incomplete = nil, message_id = nil, options = {})
      data = options
      data[:email] = email
      data[:items] = items

      if incomplete != nil
        data[:incomplete] = incomplete.to_i
      end

      if message_id != nil
        data[:message_id] = message_id
      end
      api_post(:purchase, data)
    end
params:
   email, String
   items, Array of Hashes
   incomplete, Integer
   message_id, String
   options, Hash
 returns:
   hash, response from server

 Record that a user has made a purchase, or has added items to their purchase total.