Read the odd startup option from org-mode files.

src/context/global_settings.rs

@@ -22,6 +22,11 @@ pub struct GlobalSettings<'g, 's> {
     ///
     /// Corresponds to the tab-width elisp variable.
     pub tab_width: IndentationLevel,
+
+    /// Whether to only allow odd headline levels.
+    ///
+    /// Corresponds to org-odd-levels-only elisp variable.
+    pub odd_levels_only: HeadlineLevelFilter,
 }
 
 impl<'g, 's> GlobalSettings<'g, 's> {
@@ -35,6 +40,7 @@ impl<'g, 's> GlobalSettings<'g, 's> {
             complete_todo_keywords: BTreeSet::new(),
             org_list_allow_alphabetical: false,
             tab_width: 8,
+            odd_levels_only: HeadlineLevelFilter::OddEven,
         }
     }
 }
@@ -44,3 +50,9 @@ impl<'g, 's> Default for GlobalSettings<'g, 's> {
         GlobalSettings::new()
     }
 }
+
+#[derive(Debug, Clone)]
+pub enum HeadlineLevelFilter {
+    Odd,
+    OddEven,
+}