feat(document): add $ignore to make a path ignored

Re: #4480

lib/document.js

@@ -962,6 +962,23 @@ Document.prototype.unmarkModified = function(path) {
   this.$__.activePaths.init(path);
 };
 
+/**
+ * Don't run validation on this path or persist changes to this path.
+ *
+ * ####Example:
+ *
+ *     doc.foo = null;
+ *     doc.$ignore('foo');
+ *     doc.save() // changes to foo will not be persisted and validators won't be run
+ *
+ * @param {String} path the path to ignore
+ * @api public
+ */
+
+Document.prototype.$ignore = function(path) {
+  this.$__.activePaths.ignore(path);
+};
+
 /**
  * Returns the list of paths that have been modified.
  *

test/document.modified.test.js

@@ -514,7 +514,6 @@ describe('document modified', function() {
           });
     });
 
-
     it('should reset the modified state after calling unmarkModified', function(done) {
       var db = start();
       var BlogPost = db.model(modelName, collection);
@@ -556,6 +555,5 @@ describe('document modified', function() {
         });
       });
     });
-
   });
 });