Initial commit. Basic structure in place, need to implement logic.

src/kernel/exponential.rs

@@ -0,0 +1,14 @@
+use super::Kernel;
+
+pub struct Exponential {
+    var: f64,
+    l_scale: f64,
+}
+
+impl Exponential {
+    pub fn new(var: f64, l_scale: f64) -> Self {
+        Exponential { var, l_scale }
+    }
+}
+
+impl Kernel for Exponential {}