Exposed mg_send_digest_auth_request(). Exported conn->content to Lua

mongoose.h

@@ -97,6 +97,7 @@ int mg_parse_header(const char *hdr, const char *var_name, char *buf, size_t);
 void *mg_start_thread(void *(*func)(void *), void *param);
 char *mg_md5(char buf[33], ...);
 int mg_authorize_digest(struct mg_connection *c, FILE *fp);
+void mg_send_digest_auth_request(struct mg_connection *conn);
 
 #ifdef __cplusplus
 }