Improve search to also search backwards.

Hi there guys,

Lots of changes in the last weeks in the repo! Great work.

I've improved the search in the sense that I've added backwards search on pressing "N". I've also refactored some code in the search functionality, and I've managed to keep it reasonably simple.

I thought of adding something similar to "/" but that would search backwards (perhaps ">"? In an english keyboard it sort-of makes sense.), but I decided that as long as the functionality is there, we can enable it in the future if we want to.

Cheers,
Pedro