setup poetry package and pytest infrastructure

[mbjones]

In discussing the need to better package testing, we discussed the need to run unit and integration tests for all packages. This issue is to set up poetry package metadata and pytest as a testing framework and create example tests to be expanded, and provide a CONTRIBUTING.md that describes the process

• Configure poetry
• Configure pytest
• Add CONTRIBUTING.md

[mbjones]

Completed draft in sha 77ee587 with initial test setup that runs the rasterize_all(). This test takes almost a minute so should be reduced in scope. It also overwrites test data. Need to reorganize data storage.