support for dotNotation setter and options w/ tests

Code to fix #274

Allows nested or related model attributes to be set with dot-notation

For example: `person.set( 'user.name', 'Mike' );` , as in test below.

```javascript
test("'dotNotation' enabled", function(){
			var NewUser = Backbone.RelationalModel.extend({});
			var NewPerson = Backbone.RelationalModel.extend({
				dotNotation: true,
				relations: [{
					type: Backbone.HasOne,
					key: 'user',
					relatedModel: NewUser
				}]
			});
			var person = new NewPerson({
				"normal": true,
				"user.over": 2,
				user: {name: "John", "over" : 1}
			});

			person.set( 'normal', false );
			ok( person.get( 'normal' ) === false, "setting normal attributes works as usual" );

			person.set( 'user.name', 'Mike' );
			ok( person.get('user').get('name') === "Mike", "attributes of nested models can be set via dot notation: nested.attribute");
			ok( person.get('user.name') === "Mike", "attributes of nested models can be get via dot notation: nested.attribute");
		});

```
This is my first contribution to an open-source project, and I think the code could be written better by somebody with more experience; any feedback much appreciated.