make default params available to serde (#167)

* add seed param to search params

* make default params available to serde

* lints

* create defaults for enums

* lint

src/naive_bayes/gaussian.rs

@@ -78,6 +78,7 @@ impl<T: RealNumber, M: Matrix<T>> NBDistribution<T, M> for GaussianNBDistributio
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[derive(Debug, Clone)]
 pub struct GaussianNBParameters<T: RealNumber> {
+    #[cfg_attr(feature = "serde", serde(default))]
     /// Prior probabilities of the classes. If specified the priors are not adjusted according to the data
     pub priors: Option<Vec<T>>,
 }
@@ -100,6 +101,7 @@ impl<T: RealNumber> Default for GaussianNBParameters<T> {
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[derive(Debug, Clone)]
 pub struct GaussianNBSearchParameters<T: RealNumber> {
+    #[cfg_attr(feature = "serde", serde(default))]
     /// Prior probabilities of the classes. If specified the priors are not adjusted according to the data
     pub priors: Vec<Option<Vec<T>>>,
 }