feature request: parse cargo test output and provide nice summary

[Dushistov]

There is problem in interpreting results of cargo test at first glance,
for example rust-lang/cargo#4324 .

It would be nice if cargo.el parse results of cargo test,
I mean lines like test result: ok. 16 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out and at the end provide total amount of failed, ignored and filtered out tests.