Adding _.getQuery() functionality back into master

This commit adds query string parsing capabilities to undermore along with corresponding unit testing. This plugin memoizes the query string parser on the first call to speed up any subsequent readings:

```javascript
// URL: http://foo.com?a=b&foo=bar
_.getQuery() === { a: 'b', foo: 'bar' };
_.getQuery('a') === 'b';
_.getQuery('bin', 'baz') === 'baz';
_.getQuery('z') === undefined;
```