[racket-dev] Release Announcement for v5.1.2

Some initial drafts, maybe too long:

 * The download page includes distributions for 64-bit Windows, Mac OS
   X, and two Debian flavors.

 * Racket now includes a new `racket/place' library to support
   parallelism as a complement the existing `racket/future' library.
   Racket's parallel build process is now based on places instead of
   multiple OS processes.

   To a first approximation, places support share-nothing parallelism
   and message-passing communication. Places are heavyweight compared
   to futures, but they have a simpler performance model compared to
   the best-effort parallelism of futures.

 * The syntax-certificate system has been replaced by a syntax-taint
   system.

   Both certificates and taints were designed to protect otherwise
   inaccessible bindings from abuse when they appear in macro
   expansions. Taints are simpler and impose less overhead on expansion
   and bytecode marshaling. The switch to taints also closes the
   certificate system's known holes. Macros that are not implemented
   with `syntax-rules' or `define-syntax-rule', however, must
   explicitly use `syntax-protect' to protect their expansions from
   abuse.

 * The `net/url' supports HTTPS connections, but beware that HTTPS
   handling accepts any site by default (which is equivalent to
   ignoring a browser's warnings about untrusted certificates).


> * Most "body" contexts (function body, `cond', etc) accept a mix of
>   definitions and expressions.

Wasn't that in v5.0.1? Or did you have in mind the recent changes that
are not in v5.1.2? Or something else?

The others that might be mine seem too minor to include in an
announcement.