[plt-dev] Release Announcement for v4.2, second call

I left the web-server bullet alone, since you have new text from Jay,
but here's a suggestion for the rest.

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PLT Scheme version 4.2 is now available from

  http://plt-scheme.org/

Internally, this version includes a conversion from C++ to Scheme for
part of the GUI toolbox --- specifically, 25k lines of code that
implement the general text and pasteboard editor. This conversion is a
start on a larger reimplementation of the GUI toolbox. Although we
believe that this change will help make PLT Scheme better in the long
run, we must expect bugs in the short term due to porting
errors. Users should therefore be aware of the change, even though the
new implementation is meant to behave the same as previous versions.

* A new statistical profiler is now available; see the "profiler"
  manual for more information. Currently, the profiler supports only
  textual output, but future plans include a GUI interface and
  DrScheme integration.

* The `world' teachpack is now deprecated. Its replacement `universe'
  has a new interface that uses strings instead of symbols and
  characters.

* Web-server: Native continuations in serial language, soft
  state, and typos.

* DrScheme's Stepper can now jump to a selected program expression.

* New in `scheme/base': `hash-has-key?', `hash-ref!', `in-sequences',
  `in-cycle'. New in `scheme': `count', `make-list' (from
  `scheme/list'), `const' (from `scheme/function').

* Some performance improvements, including faster start-up for small
  programs. The latter is a result of delaying module invocations at
  higher phases (compile time, meta-compile time, etc.) until
  compilation is demanded at the next lower phase; this on-demand
  instantiation is per-phase, as opposed to per-module within a phase.