Remove unused format member from SPickler trait

It turns out that this member is unnecessary also in
scala-pickling.
Import binary pickle format

- The imported files have the same LOC as in scala-pickling
- Adds test whose output has been manually verified to be
  identical with the one produced by scala-pickling
Import UnpickleMacros

Also renames PBuilder.scala to PBuilderReader.scala as in
scala-pickling.
Make PBuilderReader exact copy from scala-pickling
Enable unpicklers based on more flexible AcyclicQuery

- Adds `UnpicklerMacros_impl` and `UnpickleMacros_pickleUnpickle`
  to Compat
- Primitive picklers are now also unpicklers
- Adds `UnpicklerMacros` as an `AcyclicQuery`
- Adds `unpickle` macro to trait `Pickle`
- Adds `Unpickler` trait/object, plus `GenUnpicklers` trait
- Adds dispatch logic to `AcyclicQuery`
- Makes `AcyclicQuery` more flexible using `compose` method
- Adds unpickling test with simple final case class