implement atm purchase item PUT updates and tests

This implements the last of the CRUD operations for the purchase items
within an ATM transaction.  Adding the PUT verb (or update operation)
completes the initial API implementation.  Also adds tests to ensure
the operation is working as advertized.

* TODO: move the utility test from the app directory to the util
  directory.  Also, separate the data file requirement for the
  data manager test to be contained soley in the util directory.
update to v0.0.2