Rename struct mg_connection::label -> data. Make its size configurable

mongoose.h

@@ -658,14 +658,16 @@ struct timeval {
 #define MG_ENABLE_PACKED_FS 0
 #endif
 
-// Granularity of the send/recv IO buffer growth
 #ifndef MG_IO_SIZE
-#define MG_IO_SIZE 2048
+#define MG_IO_SIZE 2048  // Granularity of the send/recv IO buffer growth
 #endif
 
-// Maximum size of the recv IO buffer
 #ifndef MG_MAX_RECV_SIZE
-#define MG_MAX_RECV_SIZE (3 * 1024 * 1024)
+#define MG_MAX_RECV_SIZE (3 * 1024 * 1024)  // Maximum recv IO buffer size
+#endif
+
+#ifndef MG_DATA_SIZE
+#define MG_DATA_SIZE 32  // struct mg_connection :: data size
 #endif
 
 #ifndef MG_MAX_HTTP_HEADERS
@@ -1057,7 +1059,7 @@ struct mg_connection {
   void *fn_data;               // User-specified function parameter
   mg_event_handler_t pfn;      // Protocol-specific handler function
   void *pfn_data;              // Protocol-specific function parameter
-  char label[50];              // Arbitrary label
+  char data[MG_DATA_SIZE];     // Arbitrary connection data
   void *tls;                   // TLS specific data
   unsigned is_listening : 1;   // Listening connection
   unsigned is_client : 1;      // Outbound (client) connection