Use of pointer-events: none; on non-svg items

[arski]

In detail.css, you apply pointer-events: none; on .rickshaw_graph .detail to ensure that tooltips don't get hovered over and thus don't prevent other tooltips from popping up..

I find that there are two issues with that:

1. pointer-events: none; shouldn't really be used for non-svg items as described in the spec
2. it's impossible to hover over the tooltip itself, which might be nice if there is a link in there or something like that..

In my opinion, the approach of disabling pointer events and setting opacity: 0 to all tooltips would work much nicer if you enabled pointer events and then replace the opacity switch with a display: none/inline switch..

Works like a charm for me and everything is as expected

Cheers

[RichardLitt]

Sounds like a good, small PR. I'll tag it as such. @arski If you'd like to PR your changes, go ahead!