Collection docs: models is not optional if options is passed in
Allow Collection.at to accept negative indexes

This allows you to do things like

```javascript
mycollection.at(-2) // get second to last, etc.
```
Add test for negative indexes in `at` method
Set correct number of assertions
Enhancing Model with isEmpty function
Adding the isEmpty function into the modelMethods
Merge pull request #3265 from tomascasas/bb-col-doc-update

Collection docs: models is not optional if options is passed in
Send correct 'at' when firing 'add' event
Merge pull request #3039 from fastest963/master

Send correct 'at' when firing 'add' event
Merge pull request #3301 from AndrewEastwood/patch-1

Enhancing Model with isEmpty function
Update README to better match backbonejs.org 

line 14 readme missing the word "with":
Backbone supplies structure to JavaScript-heavy applications by providing models key-value binding and custom events, collections...
--> on backbonejs.org reads as -->
Backbone.js gives structure to web applications by providing models with key-value binding and custom events, collections...

Also bolded models, views and collections just as they are on backbonejs.org
Merge pull request #3281 from jisaacks/master

Allow Collection.at to accept negative indexes
removed the strong tags, but kept the "with" on 14
Merge pull request #3318 from NickStefan/patch-1

Update README to better match backbonejs.org
fix flawed test
fix wrong test: collection.model must be a function
Merge pull request #3329 from hmil/fix-options-success

fix flawed test
don't just test for the presence of options, test that it points to the same object as passed in.