Add xxhash (0.6.2) package

xxHash is an extremely fast non-cryptographic hash algorithm, working at
speeds close to RAM limits.

Tested on Samsung XE50013-K01US (x86_64).

All tests passing except for the ones dependent on valgrind.
https://gist.github.com/cstrouse/23c9d5926ffc4d53430a75d97a62b74e

packages/xxhash.rb

+require 'package'
+
+class Xxhash < Package
+  version '0.6.2'
+  source_url 'https://github.com/Cyan4973/xxHash/archive/v0.6.2.tar.gz'
+  source_sha1 '303f93e57b4e1ddc627d62a3313eaab82fd11720'
+
+  def self.build
+    system "make"
+  end
+
+  def self.install
+    FileUtils.mkdir_p ["#{CREW_DEST_DIR}/usr/local/bin", "#{CREW_DEST_DIR}/usr/local/man/man1"]
+    FileUtils.cp "xxhsum", "#{CREW_DEST_DIR}/usr/local/bin/"
+    FileUtils.cp "xxhsum.1", "#{CREW_DEST_DIR}/usr/local/man/man1/"
+  end
+end