vim:keys: Improve bindings to move lines

The old bindings had problems when trying to move further than BOF, EOF.

.config/vim/vimrc.d/40-keys.vim

@@ -116,10 +116,14 @@ endif
 nnoremap Y y$
 
 " Move lines up and down while correcting the indentation
-nnoremap <A-Up> ddkP==
-nnoremap <A-Down> ddp==
-vmap <A-Up> dkPgp=gv
-vmap <A-Down> dpgp=gv
+" https://vim.fandom.com/wiki/Moving_lines_up_or_down
+" (Use arrows, as Alt-{j,k} is used by my terminal for scrollback)
+nnoremap <silent> <A-Up> :m .-2<CR>==
+nnoremap <silent> <A-Down> :m .+1<CR>==
+vnoremap <silent> <A-Up> :m '<-2<CR>gv=gv
+vnoremap <silent> <A-Down> :m '>+1<CR>gv=gv
+inoremap <silent> <A-Up> <Esc>:m .-2<CR>==gi
+inoremap <silent> <A-Down> <Esc>:m .+1<CR>==gi
 
 " Fix & command to also use last flags
 nnoremap & :&&<CR>