Major changes, including Brotli and Lizard

- update of zstd-mt library
- add brotli v0.6.0
- add lizard v2.0
- xxhash is from zstd for lz4, lz5 and lizard now
- update also the documentation, where needed

C/brotli/br_cluster.c

@@ -0,0 +1,56 @@
+/* Copyright 2013 Google Inc. All Rights Reserved.
+
+   Distributed under MIT license.
+   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+/* Functions for clustering similar histograms together. */
+
+#include "./enc/cluster.h"
+
+#include "types.h"
+#include "./enc/bit_cost.h"  /* BrotliPopulationCost */
+#include "./enc/fast_log.h"
+#include "./enc/histogram.h"
+#include "./enc/memory.h"
+#include "./enc/port.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+static BROTLI_INLINE BROTLI_BOOL HistogramPairIsLess(
+    const HistogramPair* p1, const HistogramPair* p2) {
+  if (p1->cost_diff != p2->cost_diff) {
+    return TO_BROTLI_BOOL(p1->cost_diff > p2->cost_diff);
+  }
+  return TO_BROTLI_BOOL((p1->idx2 - p1->idx1) > (p2->idx2 - p2->idx1));
+}
+
+/* Returns entropy reduction of the context map when we combine two clusters. */
+static BROTLI_INLINE double ClusterCostDiff(size_t size_a, size_t size_b) {
+  size_t size_c = size_a + size_b;
+  return (double)size_a * FastLog2(size_a) +
+    (double)size_b * FastLog2(size_b) -
+    (double)size_c * FastLog2(size_c);
+}
+
+#define CODE(X) X
+
+#define FN(X) X ## Literal
+#include "./enc/cluster_inc.h"  /* NOLINT(build/include) */
+#undef FN
+
+#define FN(X) X ## Command
+#include "./enc/cluster_inc.h"  /* NOLINT(build/include) */
+#undef FN
+
+#define FN(X) X ## Distance
+#include "./enc/cluster_inc.h"  /* NOLINT(build/include) */
+#undef FN
+
+#undef CODE
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}  /* extern "C" */
+#endif