AnnotationRules describes how a UAST should be annotated with `uast.Role`.

all AST nodes that implements ast.Expr.

all AST nodes that implements ast.Stmt.

ToNode is an instance of `uast.ObjectToNode`, defining how to transform an into a UAST (`uast.Node`).

Transformers is the of list `transformer.Transfomer` to apply to a UAST, to learn more about the Transformers and the available ones take a look to: https://godoc.org/gopkg.in/bblfsh/sdk.v1/uast/transformer.