Add extended NodeVisitor

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
Implement rewrite() helper

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
refactor return->goto rewrite with new visitor

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
Merge branch 'feature/rewrite-visitor' into develop
refactor ReturnToAssignment class with new visitor

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>