[Racket announcement] Racket v7.1

Racket version 7.1 is now available from

    http://racket-lang.org/

* Although it is still not part of this release, the development of
  Racket on Chez Scheme continues. We still hope and expect that
  Racket-on-Chez will be ready for production use later in the v7.x
  series, perhaps mid-2019.

* Trackpad scrolling works in more reliably in some Windows and
  Linux/Unix environments.

* New users of DrRacket will open files into new tabs (by default).

* The teaching languages support the unicode character for lambda.
  The teaching unit test framework no longer stops testing when a tested
  expression signals an error.

* A refinement to error reporting for compile-time code helps clarify
  when an syntax error is likely due to an earlier unbound identifier
  (because the unbound-identifier error otherwise must be delayed, in
  case a definition appears later).

* A `++lang <lang>` flag for `raco exe` simplifies the creation of
  executables that dynamically load `#lang <lang>` modules at run
  time.

* Typed Racket adds types for mutable and immutable vectors:
  `(Mutable-Vectorof T)`, `(Immutable-Vectorof T)`, `(Immutable-Vector T)`,
  and `(Mutable-Vector T)`. The new types are subtypes of the existing
  `Vectorof` and `Vector` types. The return types of a few standard vector
  functions use the new, more specific, types. When an immutable vector
  flows from untyped code to typed code, Typed Racket may be able to check
  the vector with a flat contract.

* The hashing functions `sha1-bytes`, `sha224-bytes`, and
  `sha256-bytes` are added to `racket/base`.

* `curry` from racket/function supports currying functions with keyword
  arguments, and `procedure-arity` and `procedure-keywords` return the
  correct result when applied to curried functions.

* Slideshow supports widescreen mode (finally!). Implement widescreen
  slides using `slideshow/widescreen` or provide the `--widescreen`
  command-line flag to Slideshow. Combine `--widescreen` with
  `--save-aspect` to make widescreen mode the default in your
  installation.

* Racket supports FreeBSD/aarch64.

* Various improvements and additions were made to the DeinProgramm
  teaching languages and their documentation.

The following people contributed to this release:
Akihide Nano, Alex Harsányi, Alex Knauth, Alexander McLin, Alexis King,
Andrew Kent, Ben Greenman, Bruno Cuconato, Chongkai Zhu, Claes Wallin,
David Benoit, Gary F. Baumgartner, Gustavo Massaccesi, Jay McCarthy,
Jens Axel Søgaard, Jérôme Martin, John Clements, Jordan Johnson, Kimball
Germane, Leif Andersen, Matthew Butterick, Matthew Flatt, Matthias
Felleisen, Mike Sperber, Milo Turner, myfreeweb, Oling Cat, Paulo Matos,
Philip McGrath, Robby Findler, Roman Klochkov, Ryan Culpepper, Sam
Caldwell, Sam Tobin-Hochstadt, Shu-Hung You, Stephen Chang, Tong-Kiat
Tan, Vincent St-Amour, Winston Weinert, and yjqww6.

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