Implemented Default for Bson, Document, and ObjectId (#82)

Added `Default` implementations
    * `Bson`, `Document`

Author: NathanFlurry

.gitignore

@@ -1,5 +1,6 @@
 target
 Cargo.lock
 .vscode
+.idea
 *~
 *.swp

src/bson.rs

@@ -79,6 +79,12 @@ pub type Array = Vec<Bson>;
 /// Alias for `OrderedDocument`.
 pub type Document = OrderedDocument;
 
+impl Default for Bson {
+    fn default() -> Self {
+        Bson::Null
+    }
+}
+
 impl Debug for Bson {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {

src/ordered.rs

@@ -60,6 +60,12 @@ pub struct OrderedDocument {
     inner: LinkedHashMap<String, Bson>,
 }
 
+impl Default for OrderedDocument {
+    fn default() -> Self {
+        Document::new()
+    }
+}
+
 impl Display for OrderedDocument {
     fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
         try!(write!(fmt, "{{"));

tests/modules/bson.rs

@@ -1,12 +1,15 @@
+extern crate serde_json;
+
 use bson::{Bson, Document};
+use self::serde_json::Value;
 
 #[test]
 fn to_json() {
     let mut doc = Document::new();
     doc.insert("first", Bson::I32(1));
     doc.insert("second", Bson::String("foo".to_owned()));
     doc.insert("alphanumeric", Bson::String("bar".to_owned()));
-    let data = Bson::Document(doc).to_json();
+    let data: Value = Bson::Document(doc).clone().into();
 
     assert!(data.is_object());
     let obj = data.as_object().unwrap();
@@ -23,3 +26,16 @@ fn to_json() {
     assert!(alphanumeric.is_string());
     assert_eq!(alphanumeric.as_str().unwrap(), "bar");
 }
+
+#[test]
+fn bson_default() {
+    let bson1 = Bson::default();
+    assert_eq!(bson1, Bson::Null);
+}
+
+#[test]
+fn document_default() {
+    let doc1 = Document::default();
+    assert_eq!(doc1.keys().count(), 0);
+    assert_eq!(doc1, Document::new());
+}

tests/modules/encoder_decoder.rs

@@ -1,6 +1,3 @@
-extern crate bson;
-extern crate chrono;
-
 use std::io::Cursor;
 use bson::{Bson, decode_document, encode_document};
 use bson::oid::ObjectId;