Single-file decoder script can now (optionally) create an encoder

To complement the single-file decoder a new script was added to create an amalgamated single-file of all of the Zstd source, along with examples and (simple) tests.

lib/compress/zstd_compress.c

@@ -3749,13 +3749,16 @@ static size_t ZSTD_nextInputSizeHint(const ZSTD_CCtx* cctx)
     return hintInSize;
 }
 
-static size_t ZSTD_limitCopy(void* dst, size_t dstCapacity,
-                       const void* src, size_t srcSize)
+#ifndef ZSTD_DECOMPRESS_INTERNAL_H /* zstd_decompress.c has the same function */
+MEM_STATIC size_t ZSTD_limitCopy(void* dst, size_t dstCapacity, const void* src, size_t srcSize)
 {
     size_t const length = MIN(dstCapacity, srcSize);
-    if (length) memcpy(dst, src, length);
+    if (length > 0) {
+        memcpy(dst, src, length);
+    }
     return length;
 }
+#endif
 
 /** ZSTD_compressStream_generic():
  *  internal function for all *compressStream*() variants