Minimize struct copying

by using pointer func receivers and slices of struct pointers where possible.

help.go

@@ -74,7 +74,7 @@ OPTIONS:
    {{end}}{{end}}
 `
 
-var helpCommand = Command{
+var helpCommand = &Command{
 	Name:      "help",
 	Aliases:   []string{"h"},
 	Usage:     "Shows a list of commands or help for one command",
@@ -90,7 +90,7 @@ var helpCommand = Command{
 	},
 }
 
-var helpSubcommand = Command{
+var helpSubcommand = &Command{
 	Name:      "help",
 	Aliases:   []string{"h"},
 	Usage:     "Shows a list of commands or help for one command",
@@ -158,7 +158,15 @@ func ShowCommandHelp(ctx *Context, command string) error {
 
 // ShowSubcommandHelp prints help for the given subcommand
 func ShowSubcommandHelp(c *Context) error {
-	return ShowCommandHelp(c, c.Command.Name)
+	if c == nil {
+		return nil
+	}
+
+	if c.Command != nil {
+		return ShowCommandHelp(c, c.Command.Name)
+	}
+
+	return ShowCommandHelp(c, "")
 }
 
 // ShowVersion prints the version number of the App