Release Announcement for v8.4

[John Clements]

The release announcement sketch that I have so far is below. Please
mail me new items and/or edits.

Please phrase announcements using complete sentences and avoid the
word "now".
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* Command-line Racket provides a new expression editor by default for
its read-eval-print loop (REPL). The new REPL is based on the Chez
Scheme expression editor, but extended to use the same
language-sensitive syntax coloring and indentation tools as DrRacket.

To make Racket's REPL go back to the old editline/readline-based
editor, use the command

,input readline

and then restart Racket. Get back to the new expression editor with

,input expeditor

To toggle color mode for the new expression editor, use one of the
following, which does not require restarting Racket:

,color #false
,color #true

* Typed Racket includes a kind system.
* Racket has a `file-or-directory-stat` for unified information about
file-system objects.
* Racket on Chez has faster multiplication and division for some
numbers.
* Web server: The files dispatcher supports all standard caching-related
HTTP response headers (e.g., Cache-Control).
* Web server: A new dispatcher captures the common pattern of processing
HTTP requests and responses in a layered fashion.
* The Web Server supports use of the Cache-Control header, and includes
a new wrapping dispatcher.
* Expander: add "portal" syntax to support new forms of syntax object
binding.
* Documentation search is improved.
* Some hash operations support an optional `try-order?` argument
* The plot-metrics interface has documentation.
* Fonts support OpenType feature settings.
* The Gui library has improved support for Wayland.
* The computation of quadratic roots is further improved.
* Change `set/c` to support random generation
* add coloring and indentation support to the interations window
* allow languages to specify which characters are parentheses, and
adapt the keybindings based on them
* Many other bug repairs and other improvements!

The following people contributed to this release:

Alex Harsányi, Alex Knauth, Alexander Shopov, Alexis King, Andrew
Mauer-Oats, Andy Keep, Ayman Osman, Ben Greenman, Bob Burger, Bogdan
Popa, Cameron Moy, D. Ben Knoble, Fred Fu, Greg Hendershott, Gustavo
Massaccesi, Jamie Taylor, Jarhmander, Jesse Alama, Joel Dueck, John
Clements, Jordan Johnson, Laurent Orseau, Leif Andersen, Marc Burns,
Matthew Flatt, Matthias Felleisen, Mike Engelhart, Mike Sperber, Noah
Ma, Oscar Waddell, Pavel Panchekha, Philip McGrath, rgkirch, Robby
Findler, Sam Tobin-Hochstadt, Sergiu Ivanov, Sorawee Porncharoenwase,
Stefan Schwarzer, Stephen De Gabrielle, Tony Garnock-Jones, Viko Riféo,
and Zachary Mao



Link to package regressions issue for the 8.4 release:
https://github.com/racket/racket/issues/4125

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