Add some useful ex commands

[tyru]

From my vimrc comment example
https://github.com/tyru/dotfiles/blob/adff5c08f663546e93cdac3ada7d24a17dc560ce/dotfiles/.vim/vimrc#L653-L690

MapOriginal

MapOriginal j
MapOriginal k

MapPrefix

MapPrefix [n] prefix_name rhs

MapLeader

MapLeader ;

MapLocalLeader

MapLocalLeader ,

MapOp

" Map [nxo] lhs rhs
MapOp lhs rhs

MapMotion

" Map [nxo] lhs rhs
MapMotion lhs rhs

MapObject

" Map [xo] lhs rhs
MapObject lhs rhs

DisableMap

" Map [n] $ <Nop>
" Map [n] % <Nop>
" .
" .
" .
DisableMap [n] $ % & ' ( ) ^

MapCount

" Map -expr [n] <C-n> v:count1 . 'gt'
MapCount [n] <C-n> gt