[MacroAnnotation] Support overloads as seperate methods

[DavidDudson]

Consider whether this becomes worth it. Or whether the user should just use Tree as the input param

object someMacro() {
    def apply(val: Defn.Val) = ???
    def apply(clazz: Defn.Class) = ???
}

becomes (boilerplate removed)

inline def apply(a: Any) {
   a match {
      case _: Defn.Val => ???
      case _: Defn.Class => ???
   }
}