Pages: Upgade guide to QUnit 2.x

Fixes #86 

First draft for an upgrade guide. There are no links to this page, yet. There are layout issues, may need to port some CSS from jqueryui.com.

Would be good to get some feedback on the format. Also, am I missing something?
We may also split these phrases in two, one for setup and teardown, the other for QUnit.push.

Following the previous paragraphs, I suggest:

```markdown
QUnit module hooks `setup` and `teardown` got renamed to `beforeEach` and `afterEach`, respectivelly.

`QUnit.push()` is now found at `assert.push()`, as the assert is the argument in test callbacks.
```