Basic AST

`Select` feels a bit more idiomatic for me. It's also a common choice, e. g. Java: https://github.com/loverdos/javac-openjdk7/blob/master/src/main/java/openjdk7/com/sun/source/tree/MemberSelectTree.java or Scala: https://github.com/scala/scala/blob/2.11.x/src/reflect/scala/reflect/api/Trees.scala#L2204