Introduce the tab_width setting and give tabs a greater value when counting indentation level.

src/context/global_settings.rs

@@ -2,6 +2,7 @@ use std::collections::BTreeSet;
 
 use super::FileAccessInterface;
 use super::LocalFileAccessInterface;
+use crate::types::IndentationLevel;
 use crate::types::Object;
 
 // TODO: Ultimately, I think we'll need most of this: https://orgmode.org/manual/In_002dbuffer-Settings.html
@@ -16,6 +17,11 @@ pub struct GlobalSettings<'g, 's> {
     ///
     /// Corresponds to the org-list-allow-alphabetical elisp variable.
     pub org_list_allow_alphabetical: bool,
+
+    /// How many spaces a tab should be equal to.
+    ///
+    /// Corresponds to the tab-width elisp variable.
+    pub tab_width: IndentationLevel,
 }
 
 impl<'g, 's> GlobalSettings<'g, 's> {
@@ -28,6 +34,7 @@ impl<'g, 's> GlobalSettings<'g, 's> {
             in_progress_todo_keywords: BTreeSet::new(),
             complete_todo_keywords: BTreeSet::new(),
             org_list_allow_alphabetical: false,
+            tab_width: 8,
         }
     }
 }