[WIP] Add option to output cross-correlation * abs(cross-correlation)

[calum-chamberlain]

What does this PR do?

This will add the option to output correlation x abs(correlation) as demonstrated by Gibbons et al. (XXXX).

Why was it initiated? Any relevant Issues?

PR Checklist

• develop base branch selected?
• This PR is not directly related to an existing issue (which has no PR yet).
• All tests still pass.
• Any new features or fixed regressions are be covered via new tests.
• Any new or changed features have are fully documented.
• Significant changes have been added to CHANGES.md.
• First time contributors have added your name to CONTRIBUTORS.md.