Version 3 changes:
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-- Added two items to the appendix: (1) alternative proof that the
   optimal number of rows for JL is Theta(eps^{-2}*log(1/delta)),
   and (2) derandomized JL family with seed length O(log d +
   log(1/eps)*log(1/delta) + log(1/delta)*loglog(1/delta)). (12/7/2010)
-- Switched the proof for bounding the operator norm to an arguably
   simpler one. (12/7/2010)
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Version 2 changes:
-----------------

-- Improved introduction and related work section, and fixed various
   typos. (7/7/2010)
-- Added a warmup section, Section 4, which gives a short proof of the
   Johnson-Lindenstrauss lemma. (7/8/2010)