c,python: Add the 'b' pattern for base64 encoded strings

Change the default pattern to use a short base64 string at the end.
This increses the used bits to generate a password from 65 to 73.

c/passgeny/src/passgeny.c

@@ -21,13 +21,18 @@
 /*
  * The default pattern used for password generation
  */
-#define PASSGENY_DEFAULT_PATTERN "^6p^6p^6ps2p100d"
+#define PASSGENY_DEFAULT_PATTERN "^6p^6p^6ps3bd"
 
 /*
  * List of special characters (order is important)
  */
 #define PASSGENY_SPECIAL " +-./=_"
 
+/*
+ * base64 characters
+ */
+#define PASSGENY_BASE64 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
+
 /*
  * Argon2 parameters
  */
@@ -235,6 +240,21 @@ bool passgeny_generate(
 
             passgeny_gen_str(cword, clen + 1, "0123456789abcdef", &bh);
         }
+        else if (passgeny_patmatch(&ppat, "([0-9]*)b", popt, sizeof(popt)))
+        {
+            size_t clen = atoi(popt);
+            if (clen >= sizeof(cword))
+            {
+                fprintf(stderr, "Invalid base64 string length: %zd\n", clen);
+                return false;
+            }
+            else if (clen == 0)
+            {
+                clen = 1;
+            }
+
+            passgeny_gen_str(cword, clen + 1, PASSGENY_BASE64, &bh);
+        }
         else
         {
             printf("Error parsing pattern at: %s\n", ppat);