Improve tooltips

Allow tooltips in div element (currently tooltips only allow items in pre element which is tricky to format). Also fix wrapping, remove gradient fill, and introduce a maximum width of 500px by default.
Of course, this is an entirely subjective change and I agree it is probably best dealt with by a user-defined style - but at the same time, I think a better default style is a good thing.

Is there a file that contains the default css for .ace_tooltip or .ace_doc-tooltip ? If so, I would argue that the changes I made here are sensible defaults versus tooltips that can span the near-entire (potentially 4K screen) and that has a gradient fill background.

I tend to be someone that likes sensible defaults with the ability to override in-place of course. I don't think the current defaults are usable, which means more boilerplate for anyone wanting to use the feature.

If you are steadfast against a change in default style, then that is fine I suppose, so long as I get my div :-)