[racket-dev] Release Announcement for v5.3.4, Final Draft

The release announcement sketch that I have so far is below.  Please
mail me new items and/or edits.
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* Extflonums (80-bit floating-point numbers) are supported on some
   x86/x86_64 platforms --- including Windows, and including
   platforms where Racket is compiled to use SSE instructions for
   flonum arithmetic. Thanks to Michael Filonenko.

* DrRacket (and all of the other apps) are now signed with an
   official OS X key.

* Tally Maze: a new game based an enumeration of 2d mazes.

* The Optimization Coach DrRacket plugin has been moved from the
   Racket distribution to the Racket package repository.

* Redex: define-union-language now merges productions when languages
   define the same nonterminals. Thanks to William Bowman.

* The srfi/19 library is now compatible with the date structure type
   exported by racket/base.

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