search: improve mechanism

[lvthillo]

I know it's a bit of a vague request, but we are using this theme for an internal handbook. We recently switched to your theme instead of the old one. Thanks for your work.

Unfortunately, we receive many internal complains about the search mechanism of the theme (also when we were using the old theme, but not it starts to become a real issue). We activated the dedicated search page to make it easier but still, there are too many results shown, especially when you try to search for a combination of words or exact sentences. I'm not an Hugo expert at all, but it would be nice if the theme offers other/multiple possibilities to implement searching. The official docs describe some of them. I do understand if you see this as "overkill" but we're just looking for some improvements here. Feel free to make other recommendations.