cargo install dinghy takes too long

[gnzlbg]

I don't know if something can be done about this (if dinghy must depend on cargo then probably not), but it currently takes ~7 minutes to cargo install dinghy in travis-ci. One can use Travis cache: cargo as a workaround, but there must be a better way.

[kali]

We may be able to sever the hard coupling with cargo, but it's a bit of a refactoring, so we need to make sure it can actually be done before commiting to it. If some bits are missing, we may need to submit patches to cargo too.

[gnzlbg]

What exactly do you need from cargo? cargo metadata might provide some of it, but not all of it unfortunately :/

[kali]

That's the point really. We need an inventory of what we need, and find out which bits, if any, are missing. I think I remember that last time I looked at this, there was one bit of info that was tough to obtain (I don't remember what), so I decided... "Later."

[fredszaq]

#157 was merged and fixes this