Added exit code support

Now the exit code can be returned by BeforeFn, ActionFn and AfterFn.

The `os.Exit` function is not called by this packaged

This closes #66 and closes #164

command.go

@@ -50,7 +50,7 @@ func (c Command) FullName() string {
 }
 
 // Invokes the command given the context, parses ctx.Args() to generate command-specific flags
-func (c Command) Run(ctx *Context) error {
+func (c Command) Run(ctx *Context) (int, error) {
 	if len(c.Subcommands) > 0 || c.Before != nil || c.After != nil {
 		return c.startApp(ctx)
 	}
@@ -104,7 +104,7 @@ func (c Command) Run(ctx *Context) error {
 		fmt.Fprintln(ctx.App.Writer, "Incorrect Usage.")
 		fmt.Fprintln(ctx.App.Writer)
 		ShowCommandHelp(ctx, c.Name)
-		return err
+		return DefaultExitCode, err
 	}
 
 	nerr := normalizeFlags(c.Flags, set)
@@ -112,20 +112,19 @@ func (c Command) Run(ctx *Context) error {
 		fmt.Fprintln(ctx.App.Writer, nerr)
 		fmt.Fprintln(ctx.App.Writer)
 		ShowCommandHelp(ctx, c.Name)
-		return nerr
+		return DefaultExitCode, nerr
 	}
 	context := NewContext(ctx.App, set, ctx)
 
 	if checkCommandCompletions(context, c.Name) {
-		return nil
+		return 0, nil
 	}
 
 	if checkCommandHelp(context, c.Name) {
-		return nil
+		return 0, nil
 	}
 	context.Command = c
-	c.Action(context)
-	return nil
+	return c.Action(context), nil
 }
 
 func (c Command) Names() []string {
@@ -148,7 +147,7 @@ func (c Command) HasName(name string) bool {
 	return false
 }
 
-func (c Command) startApp(ctx *Context) error {
+func (c Command) startApp(ctx *Context) (int, error) {
 	app := NewApp()
 
 	// set the name and usage