Support reading category from in-buffer-settings.

src/parser/document.rs

@@ -191,7 +191,7 @@ fn _document<'b, 'g, 'r, 's>(
         remaining,
         Document {
             source: source.into(),
-            category: None,
+            category: context.get_global_settings().category.clone(),
             path: None,
             zeroth_section,
             children,

src/parser/in_buffer_settings.rs

@@ -111,6 +111,14 @@ pub(crate) fn apply_in_buffer_settings<'g, 's, 'sf>(
         }
     }
 
+    // Category
+    for kw in keywords
+        .iter()
+        .filter(|kw| kw.key.eq_ignore_ascii_case("category"))
+    {
+        new_settings.category = Some(kw.value.to_owned());
+    }
+
     Ok(new_settings)
 }