Rename function factories create_cut() and create_test()

[jdblischak]

Follow-up to #201 and #215.

Based on our internal discussion on how to name these functions, I propose renaming the function factories create_cut() and create_test(), and renaming their corresponding sim_gs_n() arguments to cuts cut and tests test.

[keaven]

Concept is great. I have not reviewed code or tests.

[LittleBeannie]

Thanks, @jdblischak ! I only have 1 minor comment.

[nanxstats]

OK let's get this merged! I appreciate the simplification efforts