Add pre-created data directory for test-data.

To test a DataStorer class that I'm currently working on, I need
a storage place for test-data that the tests will fetch and store.

Typically this is something that could be created by a build system,
however since I'm not familiar with build systems for Python projects,
I'm taking the lazy route on this front.  I plan to fix this in the
future when I add a setup.py or other build mechanism for this
project, but for now the time investment and learning-curve don't
make this economical.