Get rid of mg_*asprintf

src/log.h

@@ -2,13 +2,14 @@
 
 #include "arch.h"
 #include "config.h"
+#include "fmt.h"
 
 enum { MG_LL_NONE, MG_LL_ERROR, MG_LL_INFO, MG_LL_DEBUG, MG_LL_VERBOSE };
 void mg_log(const char *fmt, ...);
 bool mg_log_prefix(int ll, const char *file, int line, const char *fname);
 void mg_log_set(int log_level);
 void mg_hexdump(const void *buf, size_t len);
-void mg_log_set_fn(void (*logfunc)(unsigned char ch));
+void mg_log_set_fn(mg_pfn_t fn, void *param);
 
 #if MG_ENABLE_LOG
 #define MG_LOG(level, args)                                                \