modes:single|pair: make fields of Single and Pair public

So strange that this isn't default for tuple-like constructors.  I can
kinda get it for record-like constructors, but not for this.  Better
safe than sorry I guess?

src/modes/single.rs

@@ -1,7 +1,7 @@
 use crate::card::Card;
 
 #[derive(PartialEq, Eq, PartialOrd, Ord, Debug, Copy, Clone)]
-pub struct Single(Card);
+pub struct Single(pub Card);
 
 impl Single {
     /** Create a new single from a card `c`.  Will return None if a Single