Cookiejar module

This is an implementation of the cookie jar implementation described in issue https://github.com/ariya/phantomjs/issues/11417

The instance static method of CookieJar was removed and the constructor was made public.
A cookiejar.js module was added that adds a API for creating a cookiejar.

To use:
```javascript
var jar = require('cookiejar').create('~/cookiejar');
var page = require('webpage');
page.cookieJar = jar;
// Do Stuff...
page.close();
jar.close();
```

I would love any suggestions or comments you might have.
Hope this helps.