document scan_urlencoded2

CHANGES

@@ -2,6 +2,8 @@
   uh, the scope_id detection #defined the wrong constant.  libowfat
     always thought there was no scope_id.  Oops.
   #include <unistd.h> in io/io_sendfile.c (broken OpenBSD, thx Rob)
+  add scan_urlencoded2 (like scan_urlencoded but will not convert '+' to
+    ' '; needed for web servers, so they can serve libstdc++.tar.gz)
 
 0.21:
   errno cleanup and man page updates (Rolf Eike Beer)

t.c

@@ -25,6 +25,10 @@
      __asm__ __volatile__ ("rdtsc" : "=a" (low) : : "edx")
 
 int main(int argc,char* argv[]) {
+  char dest[1024];
+  unsigned long len;
+  scan_urlencoded2("libstdc++.tar.gz",dest,&len);
+  buffer_putmflush(buffer_1,dest,"\n");
 #if 0
   static stralloc sa;
   stralloc_copym(&sa,"foo ","bar ","baz.\n");