Add a new setting for list of grammars to automatically preview

Author: Wliu

lib/main.coffee

@@ -84,7 +84,7 @@ module.exports =
         @destroyedItems.clear()
         return unless openPreview
 
-        grammars = atom.config.get('markdown-preview.grammars') ? []
+        grammars = atom.config.get('markdown-preview.automaticPreviewGrammars') ? []
         return unless editor.getGrammar().scopeName in grammars
 
         @addPreviewForEditor(editor, atom.workspace.paneForItem(item))

package.json

@@ -78,6 +78,15 @@
         "text.plain.null-grammar"
       ],
       "description": "List of scopes for languages for which previewing is enabled. See [this README](https://github.com/atom/spell-check#spell-check-package-) for more information on finding the correct scope for a specific language."
+    },
+    "automaticPreviewGrammars": {
+      "type": "array",
+      "order": 8,
+      "default": [
+        "source.gfm",
+        "source.litcoffee"
+      ],
+      "description": "Only automatically open previews for the given list of scopes."
     }
   }
 }