Issue 3661

* doc/modules/model_evaluation.rst in the MattpSoftware fork contains my changes for issue #3661.

* issue-3661/model_evaluation_copy_edited.rst also fixes typos I found when reading the document.

* issue-3661/model_evaluation_edit_notes.txt has the explanation for the changes in model_evaluation_copy_edited.rst, and flags a few other other items for questions.
```
Expected:
    # loss_func will negate the return value of my_custom_loss_func, 
    #  which will be np.log(2), 0.693, given the values for ground_truth 
    #  and predictions defined below.

```

To get it working, you need to add >>> in front of #