Impl kernel for [Box<dyn Kernel>; N]

examples/abcdef.rs

@@ -6,7 +6,7 @@ fn main() {
     let mut model = ks::model::Binary::new(ks::model::binary::Observation::Probit);
 
     for player in &["A", "B", "C", "D", "E", "F"] {
-        let kernel: Vec<Box<dyn ks::Kernel>> = vec![
+        let kernel: [Box<dyn ks::Kernel>; 2] = [
             Box::new(ks::kernel::Constant::new(1.0)),
             Box::new(ks::kernel::Matern52::new(0.5, 1.0)),
         ];