First set of changes to use config file instead of hard-coded settings.

src/config.rs

@@ -0,0 +1,22 @@
+use crate::{gtfs, renderer};
+use std::collections::HashSet;
+extern crate serde_derive;
+extern crate serde_yaml;
+
+struct Error {
+    message: String
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+struct Config {
+    #[serde(rename = "gtfs")]
+    pub gtfs_prefs: gtfs::structs::Preferences,
+
+    #[serde(rename = "screen")]
+    pub screen_prefs: renderer::structs::Prefs,
+}
+
+
+pub fn load_config(config_name: String) -> Result<Config, Error> {
+    return Err(Error { message: String::from("Foo") });
+}