Make API a bit prettier

tests/binary-1.rs

@@ -4,7 +4,7 @@ use kickscore as ks;
 
 #[test]
 fn binary_1() {
-    let mut model = ks::model::Binary::new(ks::model::binary::Observation::Probit);
+    let mut model = ks::model::Binary::probit();
 
     let k_audrey = ks::kernel::Matern52::new(1.0, 2.0);
     let k_benjamin = ks::kernel::Matern52::new(1.0, 2.0);

tests/kickscore-basics.rs

@@ -5,7 +5,7 @@ use kickscore as ks;
 
 #[test]
 fn kickscore_basic() {
-    let mut model = ks::model::Binary::new(ks::model::binary::Observation::Probit);
+    let mut model = ks::model::Binary::probit();
 
     let k_spike = ks::kernel::Constant::new(0.5);
     let k_tom = ks::kernel::Exponential::new(1.0, 1.0);

tests/nba-history.rs

@@ -58,7 +58,7 @@ fn nba_history() {
 
     let seconds_in_year = 365.25 * 24.0 * 60.0 * 60.0;
 
-    let mut model = ks::model::Binary::new(ks::model::binary::Observation::Probit);
+    let mut model = ks::model::Binary::probit();
 
     for team in teams {
         let kernel = (