Added generator script and simple test

The script will combine decompressor sources into a single file. The example shows this in use.

contrib/declib/README.md

+# Single File Zstandard Decompression Library
+
+Create the file using the shell script:
+```
+cd zstd/contrib/declib
+./combine.sh -r "../../lib ../../lib/common ../../lib/decompress" zstddeclib-in.c > zstddeclib.c
+```
+Then add the resulting file to your project (see the [test sources](tests) for examples).

contrib/declib/combine.sh

+#!/bin/bash
+
+# Tool to bundle multiple C/C++ source files, inlining any includes.
+
+# Common file roots
+ROOTS="./"
+
+# Files previously visited
+FOUND=""
+
+# Prints the script usage then exits
+function usage {
+  echo "Usage: $0 [-r <paths>] infile"
+  echo "  -r file root search paths"
+  echo "Example: $0 -r \"../my/path ../my/other\" in.c > out.c"
+  exit 1
+}
+
+# Tests if list $1 has item $2
+function list_has_item {
+  local list="$1"
+  local item="$2"
+  if [[ $list =~ (^|[[:space:]]*)"$item"($|[[:space:]]*) ]]; then
+    return 0
+  fi
+  return 1
+}
+
+# Adds the contents of $1 with any of its includes inlined
+function add_file {
+  # Match the path
+  local file=
+  for root in $ROOTS; do
+    if test -f "$root/$1"; then
+      file="$root/$1"
+    fi
+  done
+  if [ "$file" != "" ]; then
+    # Read the file
+    local line
+    while IFS= read -r line; do
+      if [[ $line =~ ^[[:space:]]*\#[[:space:]]*include[[:space:]]*\"(.*)\".* ]]; then
+        # We have an include directive
+        local inc=${BASH_REMATCH[1]}
+        if ! `list_has_item "$FOUND" "$inc"`; then
+          # And we've not previously encountered it
+          FOUND="$FOUND $inc"
+          echo "/**** start inlining $inc ****/"
+          add_file $inc
+          echo "/**** ended inlining $inc ****/"
+        else
+          echo "/**** skipping file: $inc ****/"
+        fi
+      else
+        # Otherwise write the source line
+        echo "$line"
+      fi
+    done < "$file"
+  else
+    echo "#error Unable to find \"$1\""
+  fi
+}
+
+while getopts ":r:" opts; do
+  case $opts in
+  r)
+    ROOTS="$ROOTS $OPTARG"
+    ;;
+  *)
+    usage
+    ;;
+  esac
+done
+shift $((OPTIND-1))
+
+if [ "$1" != "" ]; then
+  add_file $1
+else
+  usage
+fi

contrib/declib/zstddeclib-in.c

+/**
+ * \file zstddeclib.c
+ * Single-file Zstandard decompressor.
+ * 
+ * Generate using:
+ * \code
+ *	makelib.sh -r "../../lib ../../lib/common ../../lib/decompress" zstddeclib-in.c > zstddeclib.c
+ * \endcode
+ */
+/* 
+ * BSD License
+ * 
+ * For Zstandard software
+ * 
+ * Copyright (c) 2016-present, Facebook, Inc. All rights reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * * Redistributions of source code must retain the above copyright notice,
+ *   this list of conditions and the following disclaimer.
+ * 
+ * * Redistributions in binary form must reproduce the above copyright notice,
+ *   this list of conditions and the following disclaimer in the documentation
+ *   and/or other materials provided with the distribution.
+ *
+ * * Neither the name Facebook nor the names of its contributors may be used
+ *   to endorse or promote products derived from this software without
+ *   specific prior written permission.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+/*
+ * Settings to bake for the standalone decompressor.
+ */
+#define DEBUGLEVEL 0
+#define XXH_NAMESPACE ZSTD_
+#define XXH_PRIVATE_API
+#define XXH_INLINE_ALL
+#define ZSTD_LEGACY_SUPPORT 0
+#define ZSTD_LIB_COMPRESSION 0
+#define ZSTD_LIB_DEPRECATED 0
+#define ZSTD_NOBENCH
+#define ZSTD_STATIC_LINKING_ONLY
+#define ZSTD_STRIP_ERROR_STRINGS
+
+#include "debug.c"
+#include "entropy_common.c"
+#include "error_private.c"
+#include "fse_decompress.c"
+#include "xxhash.c"
+#include "zstd_common.c"
+#include "huf_decompress.c"
+#include "zstd_ddict.c"
+#include "zstd_decompress.c"
+#include "zstd_decompress_block.c"