Fix additional help topics template

The additional help topics were really hard to ever get to show.  The
required conditionals were difficult to meet and did not seem to really
be logical.

Problems I see:
1) the top level command could never have additional topics.
2) you must have at least one sibling command AND one subcommand
3) we had the AND above, but then test both conditionals a second time
4) if the sub command was runnable we wouldn't print anything
5) if the sibling commands were not runnable we wouldn't print anything
4+5) it's possible that we printed "Additional help topics:" with nothing following it
6) We always printed ourselves as a sibling in the additional info

Whew, I think I fixed all of those!  Again, using
https://github.com/eparis/readable-golang-template
I'm actually able to visualize the template and see this craziness.

The conditionals BEFORE this change:

{{if .HasParent}}
        {{if and (gt .Commands 0) (gt .Parent.Commands 1) }}
                Additional help topics:
                {{if gt .Commands 0 }}
                        {{range .Commands}}
                                {{if not .Runnable}}
                                        {{rpad .CommandPath .CommandPathPadding}} {{.Short}}
                                {{end}}
                        {{end}}
                {{end}}
                {{if gt .Parent.Commands 1 }}
                        {{range .Parent.Commands}}
                                {{if .Runnable}}
                                        {{if not (eq .Name $cmd.Name) }}
                                        {{end}}
                                        {{rpad .CommandPath .CommandPathPadding}} {{.Short}}
                                {{end}}
                        {{end}}
                {{end}}
        {{end}}
{{end}}

The conditionals AFTER this change:

{{if or (.HasHelpSubCommands) (.HasRunnableSiblings)}}
        Additional help topics:
        {{if .HasHelpSubCommands}}
                {{range .Commands}}
                        {{if not .Runnable}}
                                {{rpad .CommandPath .CommandPathPadding}} {{.Short}}
                        {{end}}
                {{end}}
        {{end}}
        {{if .HasRunnableSiblings }}
                {{range .Parent.Commands}}
                        {{if .Runnable}}
                                {{if not (eq .Name $cmd.Name) }}
                                        {{rpad .CommandPath .CommandPathPadding}} {{.Short}}
                                {{end}}
                        {{end}}
                {{end}}
        {{end}}
{{end}}

command.go

@@ -223,7 +223,7 @@ Aliases:
 
 Examples:
 {{ .Example }}
-{{end}}{{ if .HasSubCommands}}
+{{end}}{{ if .HasRunnableSubCommands}}
 
 Available Commands: {{range .Commands}}{{if .Runnable}}
   {{rpad .Name .NamePadding }} {{.Short}}{{end}}{{end}}
@@ -231,9 +231,9 @@ Available Commands: {{range .Commands}}{{if .Runnable}}
 {{ if .HasLocalFlags}}Flags:
 {{.LocalFlags.FlagUsages}}{{end}}
 {{ if .HasInheritedFlags}}Global Flags:
-{{.InheritedFlags.FlagUsages}}{{end}}{{if .HasParent}}{{if and (gt .Commands 0) (gt .Parent.Commands 1) }}
-Additional help topics: {{if gt .Commands 0 }}{{range .Commands}}{{if not .Runnable}} {{rpad .CommandPath .CommandPathPadding}} {{.Short}}{{end}}{{end}}{{end}}{{if gt .Parent.Commands 1 }}{{range .Parent.Commands}}{{if .Runnable}}{{if not (eq .Name $cmd.Name) }}
-  {{rpad .CommandPath .CommandPathPadding}} {{.Short}}{{end}}{{end}}{{end}}{{end}}{{end}}
+{{.InheritedFlags.FlagUsages}}{{end}}{{if or (.HasHelpSubCommands) (.HasRunnableSiblings)}}
+Additional help topics: {{if .HasHelpSubCommands}}{{range .Commands}}{{if not .Runnable}} {{rpad .CommandPath .CommandPathPadding}} {{.Short}}{{end}}{{end}}{{end}}{{if .HasRunnableSiblings }}{{range .Parent.Commands}}{{if .Runnable}}{{if not (eq .Name $cmd.Name) }}
+  {{rpad .CommandPath .CommandPathPadding}} {{.Short}}{{end}}{{end}}{{end}}{{end}}
 {{end}}{{ if .HasSubCommands }}
 Use "{{.Root.Name}} help [command]" for more information about a command.
 {{end}}`
@@ -787,6 +787,37 @@ func (c *Command) HasSubCommands() bool {
 	return len(c.commands) > 0
 }
 
+func (c *Command) HasRunnableSiblings() bool {
+	if !c.HasParent() {
+		return false
+	}
+	for _, sub := range c.parent.commands {
+		if sub.Runnable() {
+			return true
+		}
+	}
+	return false
+}
+
+func (c *Command) HasHelpSubCommands() bool {
+	for _, sub := range c.commands {
+		if !sub.Runnable() {
+			return true
+		}
+	}
+	return false
+}
+
+// Determine if the command has runnable children commands
+func (c *Command) HasRunnableSubCommands() bool {
+	for _, sub := range c.commands {
+		if sub.Runnable() {
+			return true
+		}
+	}
+	return false
+}
+
 // Determine if the command is a child command
 func (c *Command) HasParent() bool {
 	return c.parent != nil