lfrc.example: Remove rename, add mkdir, add "show execution result"

The mapping for `mkdir` is `C` by default, though I expect many users to change
the binding when they copy from lfrc.example. "show execution result" maps to
`` ` ``. Norton Commander & its successors map it to `<c-o>`, but I think that's
better for something opening-relatred.

The `rename` command implements something `lf` has a good built-in for, and I
think can be removed. The remaining redefinition of `open` and such teach the
user all the things that the rename example did.

Many people want a keybinding for `mkdir`. Moreover, the new example shows how
to select the newly created dir, which is a feature I like but would be too
lazy to implement myself.

Finally, whenever a `$` command gives an unexpected error, I want to see what
happened. There are many ways to do so, but the one I added here seems the
simplest and it took me a while to think of it. We could also have an option to
have `$` commands pause like `!` commands when there's an error.

etc/lfrc.example

@@ -26,6 +26,9 @@ set cursorpreviewfmt "\033[7;2m"
 # use enter for shell commands
 map <enter> shell
 
+# show the result of execution of previous commands
+map ` !true
+
 # execute current file (must be executable)
 map x $$f
 map X !$f
@@ -45,9 +48,11 @@ cmd open &{{
     esac
 }}
 
-# define a custom 'rename' command without prompt for overwrite
-# cmd rename %[ -e $1 ] && printf "file exists" || mv $f $1
-# map r push :rename<space>
+cmd mkdir %{{
+    mkdir -p -- "$1" &&
+    lf -remote "send $id select \"$1\""
+}}
+map C push :mkdir<space>""<left>
 
 # make sure trash folder exists
 # %mkdir -p ~/.trash