Give the Card an associated fn new()

So that we don't have to keep doing the `{ cells: ... ..default() }`
thing.

src/card.rs

@@ -82,6 +82,21 @@ pub struct Card {
 }
 
 impl Card {
+  /// Create a new card from the given Cell array
+  pub const fn new(cells: [Cell; 9]) -> Self {
+    Self {
+      cells,
+      nw: false,
+      n: false,
+      ne: false,
+      w: false,
+      e: false,
+      sw: false,
+      s: false,
+      se: false,
+    }
+  }
+
   /// Produces a new card by stacking another on top of this one.
   pub fn merge(self, top: Self) -> (Self, Option<Self>) {
     let mut new_card = Self::default();