Update libloading to 0.8

[ids1024]

No description provided.

[elinorbgr]

Given this would bump the MSRV, this would technically be a breaking change. But the changes in libloading for 0.8 don't have any consequence on dlib, so I'd be inclined to set the dependency as libloading = ">= 0.7, < 0.9.

However I'm not sure if that might technically still be a breaking change?

[daxpedda]

I would argue that in the strictest sense it is a breaking change, anybody doing cargo update or initializing the dependency from scratch would get the newer libloading version.

But it depends on your MSRV policy of course.

[elinorbgr]

My question is rather whether in practice it could cause trouble or not.

Though I think I'm going to decide that, if you need a rustc version as old as < 1.48, surely you can go through the trouble of setting explicitly the dependency on libloading to 0.7 in your cargo.toml.

[elinorbgr]

Done in bc1466a