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/fmt_to_array.c

@@ -0,0 +1,12 @@
+#include "array.h"
+#include "textcode.h"
+
+void fmt_to_array(unsigned long (*func)(char*,const char*,unsigned long),
+		  array* a,const char* src,unsigned long len) {
+  unsigned long needed=func(0,src,len);
+  if (array_allocate(a,1,array_bytes(a)+needed-1)) {
+    char* x=array_start(a)+array_bytes(a)-needed;
+    func(x,src,len);
+  } else
+    array_fail(a);
+}