feat: Add TOML marshalling API

examples/basic/main.go

@@ -1,4 +1,5 @@
-// Command basic demonstrates decoding a TOML document with interpres.
+// Command basic demonstrates decoding and encoding a TOML document with
+// interpres.
 package main
 
 import (
@@ -48,4 +49,10 @@ func main() {
 	for _, u := range cfg.Users {
 		fmt.Printf("user:   %-6s admin=%t\n", u.Name, u.Admin)
 	}
+
+	out, err := interpres.Marshal(cfg)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("\n--- marshal ---\n%s", out)
 }