Organized stuff and updated for relevant version of rustc

[alexpyattaev]

I've found this gem by accident and it seems to work correctly on stable rust. I suppose it would not hurt to push a relevant version out.

While organizing the tests etc I've noticed that the detection of output directory to cache artifacts is "imperfect" to say the least (which breaks e.g. cargo test when it is called for "parent" crate), maybe this can be improved? I'm just not sure what would be a better way, but parsing the compiler argument seems to be fragile.