implement extractors

As we can't use:

scala> def extractor(p: Person) = p.address.street.name
extractor: (p: Person)String

scala> val p2 = person.modify(extractor).using(_.toUpperCase)
<console>:21: error: Path must have shape: _.field1.field2.each.field3.(...)

as it's hard to analyze such complex AST, it would be great to have something like:

person.modify(_.address.street.name).get

Which will return a List of values. This will allow to reuse a path for both read and write.
My practical need is to actually check a path at one instance of case class, but modify the same path in another instance of the same case class:

val accessor = (_: Person).modify(_.address.street.name)  //"access" alias for "modify" would be also great

if(accessor(person1).get == "Functional Road") accessor(person2).setTo("Imperative Road")

Currently, I've got to hack it with vars (or alternate the model), which is not very functional...

def getter[T, U](pm: T => PathModify[T, U])(in: T): List[U] = {
   var values: List[U] = Nil //list is just in case of "each"
   pm(in).using{x =>
     values ++= x
     x
   }
   values
}

Start by tracing the existing modify and PathModify APIs, including using and setTo, to understand how paths are represented and evaluated. Define the accessor behavior described in the issue, including get returning values and reusing the same path for read and write; done means the Person example works without mutable temporary state.