Update to reflect 1.4.3 of underscore.js

Hi Viacheslav,

Find attached a mega-commit that updates your underscore-perl master branch to `v1.4.3` of underscore.js.

I've also included fixes for two of the issues raised on your bug tracker:

* [sort_by](https://github.com/vti/underscore-perl/issues/7)
* [chain doesn't work with sort](https://github.com/vti/underscore-perl/issues/6)

The commit is fat: if you'd prefer it in smaller chunks, I can do that.

All tests pass locally using perl `v5.14.2`

Cheers
Rich