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.
I suppose we can do that everywhere. Are their Mac keyboards that don't write "alt" on the option key?