add base64url support

test/textcode.c

@@ -1,7 +1,10 @@
 #include "array.h"
 #include "textcode.h"
+#include <string.h>
+#include <stdio.h>
 #include <assert.h>
 #include <unistd.h>
+#include <write12.h>
 
 array a;
 
@@ -26,5 +29,11 @@ int main() {
   buf[n]=0;
   puts(buf);
 
+  assert(fmt_base64(buf,"fnörd",6)==8 && !memcmp(buf,"Zm7DtnJk",8));
+  assert(scan_base64("Zm7DtnJk",buf,&n)==8 && n==6 && !memcmp(buf,"fnörd",6));
+  assert(fmt_base64(buf,"x",1)==4 && !memcmp(buf,"eA==",4));
+  assert(scan_base64("eA====",buf,&n)==4 && n==1 && buf[0]=='x');
+  assert(fmt_base64url(buf,"\xef\xbf\xbdx",4)==6 && !memcmp(buf,"77-9eA",6));
+  assert(scan_base64url("77-9eA",buf,&n)==6 && n==4 && !memcmp(buf,"\xef\xbf\xbdx",4));
   return 0;
 }