This is a compiler plugin that tracks things that are going on during macro expansion
and then attaches the accumulated knowledge to expanded trees as a scala.collection.immutable.Map[String, Any].
So far we only remember the symbols that have been touched during expansion, storing them as
touchedSymbols -> scala.collection.immutable.List[global.Symbol].
addCompilerPlugin("org.scalamacros" % "macrotracker" % "0.1.0" cross CrossVersion.full).