Implement filtering behaviour like RUST_BACKTRACE=short

[jdm]

rust-lang/rust#38165 looks really nice for default backtrace behaviour for panics. We should make it easy to obtain similar output from this library, too!

[fitzgen]

cc @Yamakaky

[Yamakaky]

I was thinking maybe we could stabilize a std::sys::backtrace module (name to be discussed). That way it would be easier for third-party tools to use the exact same code. Another solution would be to move the compiler code to a new crate just for backtrace handling.

See also rust-lang/rust#40264.

[alexcrichton]

Sounds reasonable to me!

I don't think we should stabilize a module in std

[alexcrichton]

Implemented in #245