[plt-dev] Release Announcement for v4.2.3, third call

The release announcement sketch that I have so far is below.  I'm
still missing opinions on including all the entries that are here, and
I'm missing entries (if any) from Robby, Ryan, and Matthew.

This is the only thing missing.

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* The unit test framework for the teaching languages provides
  `check-member-of' and `check-range' for checking "random
  functions", i.e., "functions" that may produce several different
  results for one and the same argument.

* Added a new image library, `2htdp/image'.  Significant changes
  from `htdp/image':
  - copying and pasting does not introduce jaggies
  - `equal?' comparisons are more efficient
  - added rotation & scaling
  - got rid of pinholes (new overlay, beside, above functions based
    on bounding boxes)

* The `scheme/vector' library provides common vector operations
  (also reprovided by `scheme').

* The `scheme/promise' library provides several new kinds of
  promises with alternatives execution strategies.

* New port-reading utilities: `in-port', `port->list', `file->list'.

* A new require-macro, `path-up', for requiring a file that is
  higher in the directory tree.

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[Robby]
* added support for changing toolbar buttons based on the #lang
  line, use that for #lang scribble/base

[Ryan]
* syntax/parse extensions (~var, ~literal, ~and, ~not, etc)

[Matthew]
* change _pointer to mean a reference to non-GCed memory; add
  _gcpointer
* scheme/unsafe/ops? (wasn't mentioned last time)
* upgrade Boehm GC to v7.1

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          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                    http://barzilay.org/                   Maze is Life!