Add REPL boilerplate.

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

cmd/repl/main.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/user"
+
+	"code.jmug.me/jmug/interpreter-in-go/pkg/repl"
+)
+
+func main() {
+	user, err := user.Current()
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("Hello %s, this is the Monkey programming language!\n", user.Username)
+	fmt.Println("Go ahead, type something :)")
+	repl.Start(os.Stdin, os.Stdout)
+}