Make lunr pipeline feature optionable

If we have a note "Atom", and if the user types "a" or "at", then lunr pipeline ignores searching them because they are stop words. However, turning off this feature might not be a good idea when we have tons of body texts. So we turn it on as a default, but provide a way to turn it off as an option.

lib/notational-velocity-view.coffee

@@ -28,6 +28,8 @@ class NotationalVelocityView extends SelectListView
       @populateList() if @documentsLoaded
     @docQuery.on "removed", (fileDetails) =>
       @populateList() if @documentsLoaded
+    if !atom.config.get('nvatom.enableLunrPipeline')
+      @docQuery.searchIndex.pipeline.reset()
 
   isCursorProceeded: ->
     editor = @filterEditorView.model

lib/notational-velocity.coffee

@@ -9,6 +9,11 @@ module.exports =
       description: 'The directory to archive notes'
       type: 'string'
       default: path.join(process.env.ATOM_HOME, 'nvatom-notes')
+    enableLunrPipeline:
+      title: 'Enable Lunr Pipeline'
+      description: 'Lunr pipeline preprocesses query to make search faster. However, it will skip searching some of stop words such as "an" or "be".'
+      type: 'boolean'
+      default: true
 
   notationalVelocityView: null