Replace BUFSIZ with HCBUFSIZ and move them from stack to heap

include/common.h

@@ -101,13 +101,12 @@ typedef uint64_t u64;
 
 typedef uint32_t uint; // we need to get rid of this sooner or later, for consistency
 
-#define EXEC_CACHE   128
+#define EXEC_CACHE    128
 
-#define SPEED_CACHE  128
-#define SPEED_MAXAGE 4096
+#define SPEED_CACHE   128
+#define SPEED_MAXAGE  4096
 
-#undef  BUFSIZ
-#define BUFSIZ 8192
+#define HCBUFSIZ      0x10000 // general large space buffer size in case the size is unknown at compile-time
 
 /**
  * functions