task/ta-nst-011-02 -- write out to a CSV file

nparcel/writer.py
* new attributes "headers" and "write_headers"
* new class callable __call__ that prepares a DictWriter object and
  write out data to a CSV file
Merge branch 'feature/us-nst-011' of https://github.com/loum/nparcel into feature/us-nst-011
task/ta-nst-011-03 -- raw row-based results cleansing

nparcel/uncollected.py
* new method _cleanse() that at this time simply prepends "=" to the
  "CONNOTE_NBR", "BARCODE" and "ITEM_NBR columns