Feature request: very verbose log output

[liss-h]

Hi there, it would be really handy if cargo-chef had a "very verbose" (-vv = very verbose/build.rs output) flag like cargo itself.

So that when you are building complex C dependencies it doesn't seem like the build process got stuck somewhere (idk if you can relate).

If you want me to I can also have a look at the codebase and open a PR :)