Add sm3 demos and sm3_hmac bug fix

demos/sm3/sm3_kdf_demo.c

@@ -0,0 +1,28 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <gmssl/sm3.h>
+
+
+int main(void)
+{
+	SM3_KDF_CTX kdf_ctx;
+	unsigned char key[16] = {0};
+	unsigned char raw[32] = {
+		0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38,
+		0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38,
+	};
+	int i;
+
+	sm3_kdf_init(&kdf_ctx, sizeof(key));
+	sm3_kdf_update(&kdf_ctx, raw, sizeof(raw));
+	sm3_kdf_finish(&kdf_ctx, key);
+
+	printf("key: ");
+	for (i = 0; i < sizeof(key); i++) {
+		printf("%02X", key[i]);
+	}
+	printf("\n");
+
+	return 0;
+}