Add a config option for org-list-allow-alphabetical.

This fixes an issue where lines in a paragraph were incorrectly getting identified as lists because I had defaulted to assuming alphabetical bullets were allowed.

src/context/global_settings.rs

@@ -12,6 +12,10 @@ pub struct GlobalSettings<'g, 's> {
     pub file_access: &'g dyn FileAccessInterface,
     pub in_progress_todo_keywords: BTreeSet<String>,
     pub complete_todo_keywords: BTreeSet<String>,
+    /// Set to true to allow for plain lists using single letters as the bullet in the same way that numbers are used.
+    ///
+    /// Corresponds to the org-list-allow-alphabetical elisp variable.
+    pub org_list_allow_alphabetical: bool,
 }
 
 impl<'g, 's> GlobalSettings<'g, 's> {
@@ -23,6 +27,7 @@ impl<'g, 's> GlobalSettings<'g, 's> {
             },
             in_progress_todo_keywords: BTreeSet::new(),
             complete_todo_keywords: BTreeSet::new(),
+            org_list_allow_alphabetical: false,
         }
     }
 }