Make build_query a generic and implement methods

[imanuelcostigan]

build_query() calls sql_select() to pull together the SQL statement that is passed to a Query constructor. The sql_select() method is generic and can have connection specific methods. However, build_query() is not. Would it make sense to make this an exported generic function so that downstream dependencies are less problematic?

[hadley]

The point of this method is to do all the complicated NSE stuff so that database backends don't have to. What would you need from the generic?

[imanuelcostigan]

I see you have deprecated build_query from master vs. v0.4.3 as well as making quite a few other changes. I will wait to see what you end up and if necessary, update request.