Implement kCTF strategy

This implementation is pretty scuffed, but its more exploratory than anything else.

example-app/config.toml

@@ -1,7 +1,10 @@
-strategy = "target_number"
+strategy = "kctf"
 
 [leading_zeroes]
 difficulty = 4
 
 [target_number]
 max_number = 10000
+
+[kctf]
+difficulty = 100