unified fmt macro!

I suggest to write all fmt_xxx(char *dest, unsigned type u)
usings a macro.  Bellow this is the file fmt_number.h

Seems that this macro produces shorter text code.  Maybe the
key is the line: do { tmp /=base; ++len; } while(tmp);\
The compiler like len=0 instead of len=1.

The compiler 
      if (base <= 10) *--s = c+'0';\
      else *--s = (c<10) ? c+'0' : c-10+'a';\
optimize this code good.

Since all is in one file, we could change easy fmt_number.h 
and this updates many fmt_*.c files automatic.

Felix, if you accept this, I have also a similar file scan_number.h
Libowfat has manpage for fmt_uint and fmt_uint.c is missing.
If you like this macro, please include it also in fmt.h.
Then we could write similar functions easy.  I didn't test
the functions below for speed.

/nv

----------------------- fmt_number.h -------------------
#include "fmt.h"

#define fmt_number_macro(f,type,base) \
size_t f(char *s, type u) {\
  type tmp=u;\
  unsigned int len=0;\
  do { tmp /=base; ++len; } while(tmp);\
  if (s) {\
    s +=len;\
    do {\
      unsigned char c = u%base;\
      if (base <= 10) *--s = c+'0';\
      else *--s = (c<10) ? c+'0' : c-10+'a';\
      u /=base;\
    } while (u);\
  }\
  return len;\
}
--------------------------------------------------------

some applications:

------------------------- fmt_ulong.c ------------------
#include "fmt_number.h"
fmt_number_macro(fmt_ulong, unsigned long, 10)
--------------------------------------------------------

------------------------- fmt_xlong.c ------------------
#include "fmt_number.h"
fmt_number_macro(fmt_xlong, unsigned long, 16)
--------------------------------------------------------

------------------------- fmt_8long.c ------------------
#include "fmt_number.h"
fmt_number_macro(fmt_8long, unsigned long, 8)
--------------------------------------------------------

------------------------- fmt_ulonglong.c --------------
#include "fmt_number.h"
fmt_number_macro(fmt_ulonglong, unsigned long long, 10)
--------------------------------------------------------

------------------------- fmt_xlonglong.c --------------
#include "fmt_number.h"
fmt_number_macro(fmt_xlonglong, unsigned long long, 16)
--------------------------------------------------------

------------------------- fmt_uint.c -------------------
#include "fmt_number.h"
fmt_number_macro(fmt_uint, unsigned int, 10)
--------------------------------------------------------