Adding underline hints to rustdoc, thoughts?

What do you all think of this pull request?

I think it's a great idea. Probably worth checking in with some color-blind folks (or just running the colors through a visualization tool; I'll see if I can dig one up tomorrow and run those colors through it if someone hasn't already gotten to it), but the solid underline in particular both looks nice and suggests "clickable" to me, and that was not obvious the first time I was looking at the API docs.

Please post more info about this visualization tool you're thinking of especially if you don't test it out. I'd be interested in at least knowing what it is you're talking about.

There are a few "color blindness simulators" out there that filters the colors to simulate the inability to see the difference between certain hues. I can't seem to find the online one I used in the past to filter websites, but there should be one...

Regarding this change: I'm all for it. It can sometimes be hard to know what can be clicked and a subtle underline, and maybe some hover feedback, changes everything. Not having them in the text feels slightly inconsistent, though, but they should probably be obvious enough.