Subquery alias support

I really like your SQL generator (I've really tested all of them ...).
I want to use it in project algorest (https://github.com/algotronic/algorest/tree/v2), but there are some crucial features I need. One of them is aliasing of subquery in FROM clause.

I've added .as() method to Select statement prototype. I'm aware of discussion about aliasing subqueries in Issues page but nothing has happened for 3 months and I think this solution is acceptable and maps directly to SQL syntax..