Vanilla js improvements

The last commit is a bit big. I'd recommend looking at the overall pull request diff instead. Git and I weren't best friends today. :(

This pull request includes the following changes:

1. The todo filter function `_setFilter` is able to be greatly simplified just by adding a `class="selected"` to the  "All" link in index.html
2. I added a scope argument to the `$` and `$$` helper functions. This simplifies cases in view.js where a scope other than `document` is used.
3. I renamed the `$` and `$$` functions to `qsa` and `qs` respectively so as to eliminate ambiguity.
4. I cached the this value in many function handlers as `var that = this;` to avoid plaguing view.js with `Fn#bind`
5. I made `$live` call callbacks with `event.target` as the `this` value. No more `el = event.target` in event handlers!