Rename #[serde(alias)] to #[serde(rename)] and add tests

Closes #9 and #47.

tests/test_annotations.rs

@@ -0,0 +1,40 @@
+#![feature(custom_attribute, custom_derive, plugin, test)]
+#![plugin(serde_macros)]
+
+extern crate test;
+extern crate serde;
+
+use serde::json;
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+struct Default {
+    a1: i32,
+    #[serde(default)]
+    a2: i32,
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+struct Rename {
+    a1: i32,
+    #[serde(rename="a3")]
+    a2: i32,
+}
+
+#[test]
+fn test_default() {
+    let deserialized_value: Default = json::from_str(&"{\"a1\":1,\"a2\":2}").unwrap();
+    assert_eq!(deserialized_value, Default { a1: 1, a2: 2 });
+
+    let deserialized_value: Default = json::from_str(&"{\"a1\":1}").unwrap();
+    assert_eq!(deserialized_value, Default { a1: 1, a2: 0 });
+}
+
+#[test]
+fn test_rename() {
+    let value = Rename { a1: 1, a2: 2 };
+    let serialized_value = json::to_string(&value).unwrap();
+    assert_eq!(serialized_value, "{\"a1\":1,\"a3\":2}");
+
+    let deserialized_value: Rename = json::from_str(&serialized_value).unwrap();
+    assert_eq!(value, deserialized_value);
+}