Derive Eq, PartialEq, and Hash for EmailAddress

What?
=====

This enables EmailAddress equality to be checked as the current
structure only wraps two String values.

This also derives Hash, allowing it to be used as a key in dictionary
structures (e.g. BTreeMap).

rust-lib/src/email_address.rs

@@ -3,6 +3,7 @@ extern crate pest;
 extern crate pest_derive;
 use pest::{iterators::Pairs, Parser};
 use std::fmt;
+use std::hash::Hash;
 use wasm_bindgen::prelude::*;
 
 /// Options for parsing.
@@ -49,7 +50,7 @@ struct RFC5322;
 /// assert_eq!(format!("{}", email), "[email protected]");
 /// ```
 #[wasm_bindgen]
-#[derive(Debug)]
+#[derive(Debug, PartialEq, Eq, Hash)]
 pub struct EmailAddress {
     local_part: String,
     domain: String,
@@ -328,6 +329,18 @@ mod tests {
         assert_eq!(format!("{}", address), "[email protected]");
     }
 
+    #[test]
+    fn email_address_supports_equality_checking() {
+        let foo_at_bar_dot_com = EmailAddress::new("foo", "bar.com", None).unwrap();
+        let foo_at_bar_dot_com_2 = EmailAddress::new("foo", "bar.com", None).unwrap();
+        let foob_at_ar_dot_com = EmailAddress::new("foob", "ar.com", None).unwrap();
+
+        assert_eq!(foo_at_bar_dot_com, foo_at_bar_dot_com);
+        assert_eq!(foo_at_bar_dot_com, foo_at_bar_dot_com_2);
+        assert_ne!(foo_at_bar_dot_com, foob_at_ar_dot_com);
+        assert_ne!(foo_at_bar_dot_com_2, foob_at_ar_dot_com);
+    }
+
     #[test]
     fn domain_rule_does_not_parse_dash_google_dot_com() {
         let address = RFC5322::parse(Rule::domain_complete, "-google.com");