Move the support for BinaryOps from DataType to Expr

[xmnlab]

We have 2 main base ASTs: Statement (Stmt) or Expression (Expr)

The binary operation should be allowed for all expressions, and the validation for that could be moved to another layer.
Maybe astx could allows a customized layer for rules, so each flavour could define a more fine grained set of rules

[xmnlab]

We need a bit more discussion on that, as it could have a big impact.