aggregate = TRUE by default?

[wlandau]

I find aggregated flame graphs much easier to interpret, and the aggregate argument from #126 is super nice. Would it be reasonable to make aggregate = TRUE the default in print.profvis()? Are there any downsides?

[wlandau]

It's easy to set the profvis.aggregate option or the aggregate argument of the print() method once you know where to look. However, since most users expect to interact with profvis() only, I'm not sure how many would be able to find this feature on their own.