todo-writer: added --rewrite-comment-to-scaladoc support.

[cheeseng]

Added --rewrite-comment-to-scaladoc support to rewrite:

/* ... */

comment before declaration and member (trait, class, type, def, val and var) to:

/** ... */

Most of those are in compiler/, and here's one in library:

diff --git a/library/src/scala/PolyFunction.scala b/library/src/scala/PolyFunction.scala
index f37b1f9eab..46d6128276 100644
--- a/library/src/scala/PolyFunction.scala
+++ b/library/src/scala/PolyFunction.scala
@@ -2,7 +2,7 @@ package scala
 
 import language.experimental.captureChecking
 
-/* (EXPERIMENTAL) NEW DOCUMENTATION: This should be used when we stabilize erased definitions or other generalize other function types.
+/** (EXPERIMENTAL) NEW DOCUMENTATION: This should be used when we stabilize erased definitions or other generalize other function types.
  *
  * Marker trait for many (poly) function types.
  *

[bvenners]

@cheeseng You know I wonder if we should just leave those alone. Hmm. They wrote "This should be used when we stabilize erased definitions or other generalize other function types." So maybe they wanted it undocumented? Seems like maybe they just forgot to do /** though. I'll look for other instances.