Uniform usage of bold/italic tags

[kMutagene]

Replace all instances of non-markdown highlighgting (e.g. usage of quoates or double quotes) with italic or bold tags.

Makes most sense once main content is done

[Freymaurer]

I skipped through all files and documentation-principle.md was the only file still using "". Check if usage is fine or should be replaced!

[Freymaurer]

@kMutagene