Improve the vimscript code in ":h hex-editing"

Save and restore the view position before and after saving the buffer,
respectively, to keep the current view of the xxd(1)'s hex dump
unchanged after doing ":w", which previously caused the window to
scroll back to the very beginning of the buffer.  I believe it's
needless to say how annoying and counterproductive that was.

Get rid of the "Press ENTER or type command to continue" message, which
was previously displayed after opening larger binary files.  The use
of "silent" and "redraw" commands is tailored specifically to avoid
screen flickering, e.g. when doing ":w", which is caused by the buffer
being filtered by an external command.

Increase the number of octets per line, produced by xxd(1), from the
default value of 16 to 32.  This puts bigger chunks of the hex dump
on the screen and makes the whole thing much more usable.

While there, reformat the code to make it more readable, and use the
long form of the commands and variables to make the code slightly more
consistent and more understandable to newcomers.

runtime/doc/tips.txt

@@ -431,14 +431,26 @@ comma-separated list of extension(s) you find yourself wanting to edit: >
 
 	" vim -b : edit binary using xxd-format!
 	augroup Binary
-	  au!
-	  au BufReadPre  *.bin let &bin=1
-	  au BufReadPost *.bin if &bin | %!xxd
-	  au BufReadPost *.bin set ft=xxd | endif
-	  au BufWritePre *.bin if &bin | %!xxd -r
-	  au BufWritePre *.bin endif
-	  au BufWritePost *.bin if &bin | %!xxd
-	  au BufWritePost *.bin set nomod | endif
+	  autocmd!
+	  autocmd BufReadPre  *.bin set binary
+	  autocmd BufReadPost *.bin
+	    \ if &binary
+	    \ |   execute "silent %!xxd -c 32"
+	    \ |   set filetype=xxd
+	    \ |   redraw
+	    \ | endif
+	  autocmd BufWritePre *.bin
+	    \ if &binary
+	    \ |   let s:view = winsaveview()
+	    \ |   execute "silent %!xxd -r -c 32"
+	    \ | endif
+	  autocmd BufWritePost *.bin
+	    \ if &binary
+	    \ |   execute "silent %!xxd -c 32"
+	    \ |   set nomodified
+	    \ |   call winrestview(s:view)
+	    \ |   redraw
+	    \ | endif
 	augroup END
 
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