ggml : add GGML_QNT_VERSION to track quantization format changes

https://github.com/ggerganov/ggml/issues/150#issuecomment-1546625668

ggml.h

@@ -190,6 +190,9 @@
 #define GGML_FILE_MAGIC   0x67676d6c // "ggml"
 #define GGML_FILE_VERSION 1
 
+#define GGML_QNT_VERSION        1    // bump this on quantization format changes
+#define GGML_QNT_VERSION_FACTOR 1000 // do not change this
+
 #define GGML_MAX_DIMS          4
 #define GGML_MAX_NODES         4096
 #define GGML_MAX_PARAMS        256