Rotate some mappings

`<CR>`     : [except in command and quickfix windows] go to Command mode, Vim `:`, currently `a`
`' <CR>`   : "Ex" mode, Vim `g Q`, currently `A`
`<S-CR>`   : "Ex" mode, Vim `g Q`, currently `A`
`<C-CR>`   : Vim `: !`, currently `' a`
`p`        : Vim `+`, currently `<CR>`
`P`        : Vim `-`, currently `<S-CR>`
`\``       : use given register, Vim `"`, currently `p`
`~`        : start/stop recording a macro, Vim `q`, currently `P`
`aa`       : join this line with the next, Vim 'J', currently `\`\``
`aA`       : join this line with the previous, currently `\`~`
`A`        : break the line, currently `~`
`<C-S-CR>` : UNDEFINE
Add <C-x> as another key to go to Command mode
Mappings for <C-E>, <C-Y> instead of '+' and '-'

`p` : scroll line down, Vim <C-Y>
`P` : scroll line up, Vim <C-E>

No more mappings for Vim `+` and `-`.
Treat <;> and <p> keys as opposite
Last Change: 2014-03-12
Better "scroll by line"
Exchange roles of `/:?` and `m:M`

`/` : find forward, Vim `/`, currently `m`
`?` : find backward, Vim `?`, currently `M`
`m` : "Ex" mode, Vim `g Q`, currently `/`
`M` : Vim `: !`, currently `?`
Add a comment to "Observed patterns"
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
Comments: minor fix