Point: Implement hashCode

This makes Point's hashCode implementation consistent with its equals
method, and allows the use of Point as a HashMap key.

src/main/java/bagel/util/Point.java

 package bagel.util;
 
+import java.util.Objects;
+
 /**
  * Immutable class that represents a 2D point in space.
  */
@@ -42,6 +44,11 @@ public class Point {
         }
     }
 
+    @Override
+    public int hashCode() {
+        return Objects.hash(x, y);
+    }
+
     public double distanceTo(Point b) {
         return asVector().sub(b.asVector()).length();
     }