Make use of ConnectiveExpr easier

[aidin36]

Right now, there's only two `create' method for ConnectiveExpr classes: one that accepts a ConnectiveExpr_, and one that accepts FieldExpr_.

But, there should be something that accepts an array or other things. So user can write:

And(Tag("..."), Tag("..."))

Create methods cannot accept an array of Expr*, because it cannot be cast to derived classes. So, we should think of a way to solve this.

One solution is to write some overloads that accepts 2, 3, or more arguments. e.g.

And::create(FiledExpr*, FieldExpr*)

[pruthig]

Assign this one to me

[aidin36]

Yours now (: