Introduce a file access interface for reading additional files.

src/context/global_settings.rs

@@ -1,16 +1,20 @@
+use super::FileAccessInterface;
+use super::LocalFileAccessInterface;
 use crate::types::Object;
 
 // TODO: Ultimately, I think we'll need most of this: https://orgmode.org/manual/In_002dbuffer-Settings.html
 
 #[derive(Debug, Clone)]
-pub struct GlobalSettings<'g, 's> {
+pub struct GlobalSettings<'g, 's, F: FileAccessInterface> {
     pub radio_targets: Vec<&'g Vec<Object<'s>>>,
+    pub file_access: F,
 }
 
 impl<'g, 's> GlobalSettings<'g, 's> {
     pub fn new() -> Self {
         GlobalSettings {
             radio_targets: Vec::new(),
+            file_access: LocalFileAccessInterface,
         }
     }
 }