Custom ShortErrorMessageHandler manual example should use bold red for error message

[remkop]

Currently, the error message generated by this handler is rendered in the default console style.
The default handler uses bold red, which is nice.
Show users how to do this in the custom handler.

Index: docs/index.adoc
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- docs/index.adoc	(date 1594795931082)
+++ docs/index.adoc	(date 1594795931082)
@@ -2251,13 +2251,17 @@
         CommandLine cmd = ex.getCommandLine();
         PrintWriter writer = cmd.getErr();
 
-        writer.println(ex.getMessage());
+        writer.println(cmd.getColorScheme().errorText(ex.getMessage())); // error message in bold red
         UnmatchedArgumentException.printSuggestions(ex, writer);
         writer.print(cmd.getHelp().fullSynopsis()); // since 4.1
 
         CommandSpec spec = cmd.getCommandSpec();
         writer.printf("Try '%s --help' for more information.%n", spec.qualifiedName());
 
+        if ("DEBUG".equalsIgnoreCase(System.getProperty("picocli.trace"))) {
+            ex.printStackTrace(System.err); // provide more details if requested
+        }
+
         return cmd.getExitCodeExceptionMapper() != null
                     ? cmd.getExitCodeExceptionMapper().getExitCode(ex)
                     : spec.exitCodeOnInvalidInput();

[remkop]

More changes:

• rename writer to err
• print stack trace to cmd.getErr instead of to System.err
• print stack trace after DEBUG trace messages and before the red bold error message/usage message
• apply stacktrace style to stack trace

        PrintWriter err = cmd.getErr();

        // if we are tracing at DEBUG level, print a stacktrace
        if ("DEBUG".equalsIgnoreCase(System.getProperty("picocli.trace"))) {
            StringWriter sw = new StringWriter();
            ex.printStackTrace(new PrintWriter(sw, true));
            err.print(cmd.getColorScheme().stackTraceText(sw.toString()));
        }

        err.println(cmd.getColorScheme().errorText(ex.getMessage())); // bold red
        UnmatchedArgumentException.printSuggestions(ex, err);
        err.print(cmd.getHelp().fullSynopsis());

        CommandSpec spec = cmd.getCommandSpec();
        err.printf("Try '%s --help' for more information.%n", spec.qualifiedName());