Add tests for checking for extraneous leading newlines (or lack thereof)

Couldn't find a better place to put this (the "valid" and "invalid"
tests are just for parser) so I made a new test module

tests/formatting.rs

@@ -0,0 +1,52 @@
+extern crate rustc_serialize;
+extern crate toml;
+use toml::encode_str;
+
+#[derive(Debug, Clone, Hash, PartialEq, Eq, RustcEncodable, RustcDecodable)]
+struct User {
+    pub name: String,
+    pub surname: String,
+}
+
+#[derive(Debug, Clone, Hash, PartialEq, Eq, RustcEncodable, RustcDecodable)]
+struct Users {
+    pub user: Vec<User>,
+}
+
+#[derive(Debug, Clone, Hash, PartialEq, Eq, RustcEncodable, RustcDecodable)]
+struct TwoUsers {
+    pub user0: User,
+    pub user1: User,
+}
+
+#[test]
+fn no_unnecessary_newlines_array() {
+    assert!(!encode_str(&Users {
+            user: vec![
+                    User {
+                        name: "John".to_string(),
+                        surname: "Doe".to_string(),
+                    },
+                    User {
+                        name: "Jane".to_string(),
+                        surname: "Dough".to_string(),
+                    },
+                ],
+        })
+        .starts_with("\n"));
+}
+
+#[test]
+fn no_unnecessary_newlines_table() {
+    assert!(!encode_str(&TwoUsers {
+            user0: User {
+                name: "John".to_string(),
+                surname: "Doe".to_string(),
+            },
+            user1: User {
+                name: "Jane".to_string(),
+                surname: "Dough".to_string(),
+            },
+        })
+        .starts_with("\n"));
+}