Fix the Gaussian Xor and XNOR experiment and the plots.

[jdey4]

My issue is about ...
The parity experiment uses the old name PLF and the Y-axis should be changed to log-scale in order to be consistent with the main draft.

Snapshot of documentation error:

Additional context

[PSSF23]

@jdey4 https://github.com/neurodata/ProgLearn/blob/staging/docs/experiments/functions/xor_nxor_functions.py