cli: add pre_execute & post_execute

examples/cli.v

@@ -16,7 +16,9 @@ fn main() {
 	mut greet_cmd := cli.Command{
 		name: 'greet',
 		description: 'Prints greeting in different languages',
+		pre_execute: greet_pre_func,
 		execute: greet_func,
+		post_execute: greet_post_func,
 		parent: 0
 	}
 	greet_cmd.add_flag(cli.Flag{
@@ -50,3 +52,11 @@ fn greet_func(cmd cli.Command) {
 		}
 	}
 }
+
+fn greet_pre_func(cmd cli.Command) {
+	println('This is a function running before the main function')
+}
+
+fn greet_post_func(cmd cli.Command) {
+	println('This is a function running after the main function')
+}

vlib/cli/command.v

@@ -5,7 +5,9 @@ pub mut:
 	name string
 	description string
 	version string
+	pre_execute fn(cmd Command)
 	execute fn(cmd Command)
+	post_execute fn(cmd Command)
 
 	disable_help bool
 	disable_version bool
@@ -126,8 +128,18 @@ fn (cmd &Command) parse_commands() {
 	} else {
 		cmd.check_required_flags()
 
+		if int(cmd.pre_execute) > 0 {
+			pre_execute := cmd.pre_execute
+			pre_execute(cmd)
+		}
+
 		execute := cmd.execute
 		execute(cmd) // TODO: fix once higher order function can be execute on struct variable
+		
+		if int(cmd.post_execute) > 0 {
+			post_execute := cmd.post_execute
+			post_execute(cmd)
+		}
 	}
 }