See this issue: https://github.com/alsuren/cargo-quickinstall/issues/27
Quick Install is a hosted repo of built crates, essentially. The approach I've taken here is
a list of strategies:
1. First, we check the crate meta or default and build the URL to the repo. Once we have
that, we perform a `HEAD` request to the URL to see if it's available.
2. If it's not, we build the URL to the quickinstall repo, and perform a `HEAD` to there.
As soon as we've got a hit, we use that. I've built it so it's extensible with more strategies.
This could be useful for #4.
This also adds a prompt before downloading from third-party sources, and logs a short
name for a source, which is easier to glance than a full URL, and includes a quick refactor
of the install/link machinery.
