Exchange roles of `n:N` and `m:M`

`n`  : repeat "go to character", currently `m`
`N`  : repeat "go to character" in the opposite direction, currently `M`
`m` : repeat last find, Vim `n`, currently `n`
`M` : repeat last find in the opposite direction, Vim `N`, currently `N`
Move around comment lines
Comments: minor fix