Added documentation to Decoupled, Conditionals, Counter (#1015)

* Added documentation to Decoupled, Conditionals, Counter

* Fixed private Counter class error

* Move Counter class deprecation and re-definition into util package object.

* Revert "Move Counter class deprecation and re-definition into util package object."

This reverts commit f61bdddf7051522363e1d203fcd46b512047c87d.

* Restore the old Counter definition and address this in a separate PR.
We can move the deprecation warning and the type definition into the util package object (see f61bdddf7051522363e1d203fcd46b512047c87d), but then we fail tests using Counter with a `ScalaReflectionException` in Aggregate.scala:779 (in def cloneType) when:
`Some(mirror.reflect(this).symbol)` generates `type Counter is not a class`.

* Made @ducky64 change to Counter doc
Used to generate an inline (logic directly in the containing Module, no internal Module is created) hardware counter.