Allow `debug` expressions in redaction macros

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It can be a bit confusing when some macros have features which others don't. So this adds debug expressions to the redaction macros.

(Though the calls do get quite long; possibly we want to recommend something like description in place of debug throughout?)

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This is rebased and ready for merging / review

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I forgot about this and did it in https://github.com/mitsuhiko/insta/pull/756! so closing