[racket] Moby is obsoleted by Whalesong

In the absence of an official revokation procedure for PLaneT
packages, I've released a mock package of Moby.  It's there just to
print the following message:

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Moby is obsolete, and has been replaced with the Whalesong project.

See:

    http://hashcollision.org/whalesong

for installation and examples.

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I'll be releasing a new version of Whalesong in a few hours that will
correct a few bugs, provide hash tables, and produce smaller files.