Add file transport

examples/transport_file.rs

@@ -0,0 +1,20 @@
+extern crate lettre;
+
+use lettre::transport::file::FileEmailTransport;
+use lettre::transport::EmailTransport;
+use lettre::email::EmailBuilder;
+
+
+fn main() {
+    let mut sender = FileEmailTransport::new("/tmp/");
+    let email = EmailBuilder::new()
+                    .to("root@localhost")
+                    .from("user@localhost")
+                    .body("Hello World!")
+                    .subject("Hello")
+                    .build()
+                    .unwrap();
+    let result = sender.send(email);
+    println!("{:?}", result);
+    assert!(result.is_ok());
+}