[August 31, 2023]: [definition of 'specificity' needs to be rephrased]

[abhicc]

The current definition of 'specificity' states that it gives the False Negative Rate. Specificity actually gives the True Negative Rate.

[elletjies]

@abhicc thanks! Feel to put in a PR for our reviewers to take a further look.

[sfmig]

This seems to be fixed now:

• sensitivity is defined as True Positive rate
• specificity is defined as True Negative rate
  both of which match the wikipedia definitions.

I opened a PR #761 for crosslinking this term but I think this issue can be safely closed.