remove special case stralloc textcode functions

write generic stralloc and array textcode wrapper functions
change textcode API to use long instead of int
add cescape fmt and scan functions to textcode
add fmt_foldwhitespace to textcode

textcode/scan_to_array.c

@@ -0,0 +1,12 @@
+#include "str.h"
+#include "array.h"
+#include "textcode.h"
+
+unsigned long scan_to_array(unsigned long (*func)(const char*,char*,unsigned long*),
+			    const char* src,array* dest) {
+  unsigned long scanned;
+  unsigned long needed=str_len(src);
+  char* x=array_start(dest)+array_bytes(dest);
+  if (!array_allocate(dest,1,array_bytes(dest)+needed-1)) return 0;
+  return func(src,x,&scanned);
+}