Ignore whitespace as the default behaviour

Suggested on https://news.ycombinator.com/item?id=11376556

I think that this would be great, we have many diffs that show changed line endings that I'm not interested in.

But sometimes whitespace is significant, this would also hide that.

Making it configurable per user is not ideal.

So this is hard, but I wanted to bring it up.

/cc @dzaporozhets @JobV