First swing at adding window.history

Used [this spec](http://www.whatwg.org/specs/web-apps/current-work/multipage/history.html) as my reference.
```
 level1/core         535/535      100%
 level1/html         238/238      100%
 level1/svg          527/527      100%
 level2/core         283/283      100%
 level2/html         706/706      100%
 level2/style          15/15      100%
 level2/extra            4/4      100%
 level2/events         24/24      100%
 level3/xpath          93/93      100%
 window/index          12/12      100%
 window/script         10/10      100%
 window/console          2/2      100%
 window/frame          16/16      100%
 sizzle/index          14/14      100%
 jsdom/index           76/76      100%
 jsdom/parsing         10/10      100%
 jsdom/env             25/25      100%
 jsonp/jsonp             1/1      100%
 browser/index         34/34      100%
---------------------------------------
TOTALS: 0/2625 failed; 100% success
TIME: 39483ms
```

Added 5 exhaustive tests for the new history object. Would love thoughts / feedback. Cheers. :)