add documentaiton string for defun()

[k-okada]

DO NOT MEARGE UNTIL NEXT VACATION

see #75 for discussion

• add NULL documentation string
• add argument to defun for adding documentation string to functions written by C

[k-okada]

I tried to use optional argument as follow, but this sometimes segfaults... not sure why

#ifdef USE_STDARG
pointer defun(register context *ctx, char *name, pointer mod, pointer (*f)(), ...)
#else
pointer defun(ctx,name,mod,f)
register context *ctx;
char *name;
pointer mod;
pointer (*f)();
#endif
{ register pointer sym,pkg,pdoc;
  char* doc = NULL;
#ifdef USE_STDARG
  va_list args;
  va_start(args, f);
  doc = va_arg(args, char*);
  printf("name =%s, f=%p(%p), doc=%p\n", name, f, *f, doc);
  va_end(args);
#endif
#if defined(DEFUN_DEBUG) || defined(DEBUG_COUNT)
  static int count=0;

  count++;
#endif
#ifdef DEFUN_DEBUG
  printf( "defun:%d:%s:", count, name );
#endif
  pkg=Spevalof(PACKAGE);
  sym=intern(ctx,name,strlen(name),pkg);
#ifdef USE_STDARG
  if (doc != NULL) {
    pdoc = makestring(doc,strlen(doc));
    vpush(pdoc);
  }
  compfun(ctx, sym, mod, f, pdoc);
  if (doc != NULL) vpop();
#else
  pointer_update(sym->c.sym.spefunc,makecode(mod,f,SUBR_FUNCTION));
#endif
#ifdef DEFUN_DEBUG
  printf( "0x%lx\n", sym->c.sym.spefunc->c.code.entry );
#endif
  return(sym);}

[k-okada]

closed since this is duplicates of #116

[k-okada]

@Affonso-Gui
We have to re-compile roseus, to solve #291 problem,

• in general change of euslisp which require re-compilation of downstream package is not a good idea
• for for documentation, I think that's worth doing and this force all users to write documentation. so we should accept this idea

In order to do this.

1. merge this
2. remove macro in https://github.com/euslisp/EusLisp/pull/116/files#diff-326a8ed4a8484866ade7137571f87d54R1078

+#define defun(a, b, c, d) defun(a, b, c, d, NULL)

3. remove _defun from https://github.com/jsk-ros-pkg/jsk_roseus/blob/1.7.0/roseus/roseus.cpp#L1878

[Affonso-Gui]

@k-okada
Thanks for the explanation.
I agree with these steps, and would also be glad to start adding documentation to C defined functions.