Snappy：快速的压缩/解压缩工具

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Some of the benchmark data in testdata/ is licensed differently:

 - fireworks.jpeg is Copyright 2013 Steinar H. Gunderson, and
   is licensed under the Creative Commons Attribution 3.0 license
   (CC-BY-3.0). See https://creativecommons.org/licenses/by/3.0/
   for more information.

 - kppkn.gtb is taken from the Gaviota chess tablebase set, and
   is licensed under the MIT License. See
   https://sites.google.com/site/gaviotachessengine/Home/endgame-tablebases-1
   for more information.

 - paper-100k.pdf is an excerpt (bytes 92160 to 194560) from the paper
   “Combinatorial Modeling of Chromatin Features Quantitatively Predicts DNA
   Replication Timing in _Drosophila_” by Federico Comoglio and Renato Paro,
   which is licensed under the CC-BY license. See
   http://www.ploscompbiol.org/static/license for more ifnormation.

 - alice29.txt, asyoulik.txt, plrabn12.txt and lcet10.txt are from Project
   Gutenberg. The first three have expired copyrights and are in the public
   domain; the latter does not have expired copyright, but is still in the
   public domain according to the license information
   (http://www.gutenberg.org/ebooks/53).