Reorganize some code and add the start of the transport file parsing

src/properties/transport_fit.rs

@@ -0,0 +1,13 @@
+pub struct SpeciesTransportData {
+    pub name: String,
+    pub viscosities: Vec<TransportFit>,
+    pub conductivities: Vec<TransportFit>,
+}
+
+pub struct TransportFit {
+    pub temp_range: (f64, f64),
+    pub a: f64,
+    pub b: f64,
+    pub c: f64,
+    pub d: f64,
+}