doc - add indexes for base64url_*

doc/crypt.tex

@@ -6578,6 +6578,11 @@ ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_
 Those characters are sometimes also called URL and filename safe alphabet.
 The interface is analogous to \textit{base64\_xxxx} functions in previous chapter.
 
+\index{base64url\_encode()}
+\index{base64url\_strict\_encode()}
+\index{base64url\_decode()}
+\index{base64url\_strict\_decode()}
+\index{base64url\_sane\_decode()}
 \begin{verbatim}
 int base64url_encode(const unsigned char *in,  unsigned long len,
                                     char *out, unsigned long *outlen);