Tools: using nicer characters for showing a tree.

Especially in small trees, ASCII characters are confusing.  Use nicer
UTF-8 characters, which are more readable to the audience of this
script.  We don't expect the audience of this script to have limited
environments where these characters will not be shown, but if that
happens, we could improve the script to select the caracters based on
the locale.

Suggested-by: Liam Crilly <liam@nginx.com>
Reviewed-by: Andrew Clayton <a.clayton@nginx.com>
Signed-off-by: Alejandro Colomar <alx@nginx.com>

tools/setup-unit

@@ -42,8 +42,8 @@ SYNOPSIS
         $program_name [-h] COMMAND [ARGS]
 
     Subcommands
-        +-- repo-config  [-hn] [PKG-MANAGER OS-NAME OS-VERSION]
-        +-- welcome      [-hn]
+        ├── repo-config  [-hn] [PKG-MANAGER OS-NAME OS-VERSION]
+        └── welcome      [-hn]
 
 DESCRIPTION
         This script simplifies installing and configuring an NGINX Unit server
@@ -78,19 +78,19 @@ SYNOPSIS
         $program_name [-h] COMMAND [ARGS]
 
     Subcommands
-        +-- cmd          [-h]
-        +-- ctl          [-h] [-s SOCK] SUBCOMMAND [ARGS]
-        |   +-- http     [-h] [-c CURLOPT] METHOD PATH
-        |   +-- insert   [-h] PATH INDEX
-        +-- freeport     [-h]
-        +-- json-ins     [-hn] JSON INDEX
-        +-- os-probe     [-h]
-        +-- ps           [-h] [-t TYPE]
-        +-- repo-config  [-hn] [PKG-MANAGER OS-NAME OS-VERSION]
-        +-- sock         [-h] SUBCOMMAND [ARGS]
-        |   +-- filter   [-chs]
-        |   +-- find     [-h]
-        +-- welcome      [-hn]
+        ├── cmd          [-h]
+        ├── ctl          [-h] [-s SOCK] SUBCOMMAND [ARGS]
+        │   ├── http     [-h] [-c CURLOPT] METHOD PATH
+        │   └── insert   [-h] PATH INDEX
+        ├── freeport     [-h]
+        ├── json-ins     [-hn] JSON INDEX
+        ├── os-probe     [-h]
+        ├── ps           [-h] [-t TYPE]
+        ├── repo-config  [-hn] [PKG-MANAGER OS-NAME OS-VERSION]
+        ├── sock         [-h] SUBCOMMAND [ARGS]
+        │   ├── filter   [-chs]
+        │   └── find     [-h]
+        └── welcome      [-hn]
 
 DESCRIPTION
         This script simplifies installing and configuring
@@ -210,8 +210,8 @@ SYNOPSIS
         $program_name ctl [-h] [-s SOCK] SUBCOMMAND [ARGS]
 
     Subcommands
-        +-- http    [-h] [-c CURLOPT] METHOD PATH
-        +-- insert  [-h] PATH INDEX
+        ├── http    [-h] [-c CURLOPT] METHOD PATH
+        └── insert  [-h] PATH INDEX
 
 DESCRIPTION
         Control a running unitd(8) instance through its control API socket.
@@ -1231,8 +1231,8 @@ SYNOPSIS
         $program_name sock [-h] SUBCOMMAND [ARGS]
 
     Subcommands
-        +-- filter  [-ch]
-        +-- find    [-h]
+        ├── filter  [-ch]
+        └── find    [-h]
 
 DESCRIPTION
         Print the control API socket address of running unitd(8)