0.8.1: Merge pull request #1293 from martinholmer/file-upload-tests

Contributor	PR#	Description
Anderson Frailey	#1257	Add MTR with respect to spouse earnings
Martin Holmer	#1265	Add tax differences table to Tax-Calculator CLI --tables output
Peter Steinberg	#1198	Add testing for notebooks, starting with the behavior_example and 10-min notebooks
Matt Jensen	#1277	Update Jupyter Notebooks to demonstrate the latest Python API
Matt Jensen	#1278	Enable the charitable givings elasticity to vary by AGI bin
Zach Risher	#1179, #1285	Introduce records_variables.json, a single source of truth for records variables