message: DOC: document mem-management API changes
  Document mem-management API changes in release notes.
diff: @@ -16,6 +16,9 @@ The Axom project release numbers follow [Semantic Versioning](http://semver.org/
  ### Deprecated
  ### Changed
  +- Modified the API of Axom's memory management routines to not leak usage of Umpire. Instead of
  + passing an `umpire::Allocator` object to specify an allocator, we now use the corresponding
  + integer ID associated with the allocator.
  ### Fixed
  - Fixed usage of cuda kernel policies in Mint. Raja v0.11.0 changed the way max threads
  