Merge pull request #1256 from mslourens/export-html

first attempt to export html

lib/main-menu.js

@@ -108,6 +108,13 @@ const file = {
             mainWindow.webContents.send('list:isMarkdownNote')
             mainWindow.webContents.send('export:save-md')
           }
+        },
+        {
+          label: 'HTML (.html)',
+          click () {
+            mainWindow.webContents.send('list:isMarkdownNote')
+            mainWindow.webContents.send('export:save-html')
+          }
         }
       ]
     },