Use cond! macro where appropriate

ammend cond

Use cond! macro where appropriate
Use pattern-matching instead of conditionals where appropriate to improve code clarity
Convert various inner doc-comments to outer doc-comments

Convert various inner doc-comments to outer doc-comments

Convert various inner doc-comments to outer doc-comments
Use four-space indentation, add trailing commas, and remove unnecessary uses of the return keyword
auto merge of #6586 : bjz/rust/formatting-and-conditionals, r=thestinger