Split mg_*printf* functions into src/printf.c/h

src/fmt.h

@@ -3,13 +3,26 @@
 #include "arch.h"
 #include "iobuf.h"
 
-typedef void (*mg_pfn_t)(char, void *);                  // Custom putchar
+typedef void (*mg_pfn_t)(char, void *);                  // Output function
 typedef size_t (*mg_pm_t)(mg_pfn_t, void *, va_list *);  // %M printer
-void mg_pfn_iobuf(char ch, void *param);                 // iobuf printer
 
+// The lowest level
 size_t mg_vxprintf(void (*)(char, void *), void *, const char *fmt, va_list *);
 size_t mg_xprintf(void (*fn)(char, void *), void *, const char *fmt, ...);
+
+// Convenience wrappers around mg_xprintf
 size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list *ap);
 size_t mg_snprintf(char *, size_t, const char *fmt, ...);
 char *mg_vmprintf(const char *fmt, va_list *ap);
 char *mg_mprintf(const char *fmt, ...);
+
+// %M print helper functions
+size_t mg_print_ip(void (*out)(char, void *), void *arg, va_list *ap);
+size_t mg_print_ip_port(void (*out)(char, void *), void *arg, va_list *ap);
+size_t mg_print_ip4(void (*out)(char, void *), void *arg, va_list *ap);
+size_t mg_print_ip6(void (*out)(char, void *), void *arg, va_list *ap);
+size_t mg_print_mac(void (*out)(char, void *), void *arg, va_list *ap);
+
+// Various output functions
+void mg_pfn_iobuf(char ch, void *param);  // param: struct mg_iobuf *
+void mg_pfn_stdout(char c, void *param);  // param: ignored