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/decompress/zstd_decompress.c

@@ -1498,6 +1498,7 @@ size_t ZSTD_estimateDStreamSize_fromFrame(const void* src, size_t srcSize)
 
 /* *****   Decompression   ***** */
 
+#ifndef ZSTD_COMPRESS_H /* zstd_compress.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);
@@ -1506,7 +1507,7 @@ MEM_STATIC size_t ZSTD_limitCopy(void* dst, size_t dstCapacity, const void* src,
     }
     return length;
 }
-
+#endif
 
 size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inBuffer* input)
 {