All: Normalize keyboard interaction markup

Follow up to discussion in #218. All key commands are now wrapped in code blocks. Key combos have spaces around `+` to ease the mental parsing. There were a mix of colons and dashes between the keys and the description; I chose to normalize to the dashes since they provide additional visual spacing to ease the mental parsing.
They all do to my knowledge, but referring to the key as “option” is common, and I don't think it hurts to be explicit here.