Exchange roles of `a:A` and `v:V`

`a`  : Vim `r`, currently `v`
`A`  : Vim `R`, currently `V`
`vv` : join this line with the next, Vim `J`, currently `aa`
`vV` : join this line with the previous, currently `aA`
`V`  : break the line, currently `A`
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