first zstdmt sketch

lib/compress/zstdmt_compress.h

@@ -0,0 +1,12 @@
+
+#include <stddef.h>   /* size_t */
+
+typedef struct ZSTDMT_CCtx_s ZSTDMT_CCtx;
+
+ZSTDMT_CCtx *ZSTDMT_createCCtx(unsigned nbThreads);
+size_t ZSTDMT_freeCCtx(ZSTDMT_CCtx* cctx);
+
+size_t ZSTDMT_compressCCtx(ZSTDMT_CCtx* cctx,
+                           void* dst, size_t dstCapacity,
+                     const void* src, size_t srcSize,
+                           int compressionLevel);