More kbd shortcuts for Bf

I added a bunch of keyboard shortcuts to BottomFeeder this evening. The shortcuts are as follows:

• ctrl-b - Browse (either the feed or item)
• ctrl-l - Close the selected folder
• ctrl-n - Select next unread item
• ctrl-o - Open the selected folder
• ctrl-p - Select the previous unread item
• ctrl-r - Mark all items (in feed or folder) read
• ctrl-s - Open the search tool
• ctrl-u - Mark all items (in feed or folder) unread

Makes it a lot easier to use, that's for sure.