Add almanack score for simplified understanding through single metric

[d33bs]

Description

This PR adds a "almanack score" metric which summarizes the findings of other metrics in one single value. This score is calculated using boolean metrics and a "sustainability direction" value per metric. The values are summed and divided by the number of metrics to then provide a score. This score is intended to prepare for a more statistically profound measure on repository sustainability which is formed through modeling and other related efforts.

Along the journey towards this PR I noticed and fixed the following:

• Metrics types and type check tests for the metrics table (which presented challenges earlier and benefited the work in this PR).

References #135
Closes #207

What is the nature of your change?

• Content additions or updates (adds or updates content)
• Bug fix (fixes an issue).
• Enhancement (adds functionality).
• Breaking change (these changes would cause existing functionality to not work as expected).

Checklist

Please ensure that all boxes are checked before indicating that this pull request is ready for review.

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• I have performed a self-review of my own contributions.
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• I have made corresponding changes to related documentation (outside of book content).
• My changes generate no new warnings.
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[gwaybio]

Several discussion points this time

[d33bs]

Thanks @gwaybio for the earlier review! I've restructured the approach here with an eye towards simplification and better documentation. When there's a chance, could I ask for another look? Thank you!

[d33bs]

Thanks @gwaybio for the further review! After making some changes based on your comments here and our discussion, I wanted to make note that I've changed the language a bit within the code and in the PR description to label this score as an "almanack score" which I feel might be distinct from the "sustainability score" (or at least may need consolidation at some point in the future to better encompass the full gamut of Almanack metrics). The PR no longer closes the sustainability score issue (#135) to instead continue exploring this as we develop the Almanack.

[gwaybio]

Thanks for the great discussions in this PR! I think the project will benefit from them.

[gwaybio]

Suggested change

	# calculate sustainability score (modify placeholder)
	# calculate almanack score (the function modifies the placeholder)

[gwaybio]

Suggested change

	Computes an Almanack score by normalizing boolean Almanack
	table metrics in order to summarize analysis.
	Computes an Almanack score by counting boolean Almanack
	table metrics to provide a quick summary of software sustainability.

[gwaybio]

Is this still true?

[gwaybio]

Suggested change

	Dictionary which includes number of almanack boolean metrics
	with a non-zero sustainability correction which passed, number
	of almanack checks in total, and a score which is the number
	of passed checks divided by the total number of checks that
	represents how likely a repository will be maintained over
	time based on the existing Almanack metrics.
	Dictionary of length three, including the following: 1) number of
	Almanack boolean metrics that passed (numerator), 2) number of
	total Almanack boolean metrics considered (denominator), and 3) a
	score that represents how likely the repository will be maintained
	over time based (numerator / denominator).