Prevent CLI to panic when the pipe is broken, fixes #5

[jnioche]

No description provided.

[xoen]

I'm trying to wrap my head around this...not quite the diff itself which is relatively "clear" (use standard C library's signal() function to "set the disposition of the signal" to use the default action)

But I'm trying to figure out why this happens, this SO answer is the best explanation I've found so far.

TL;DR: it's to do with how println!() expands to use ::std::io::_print() which can panic (the answers point to the reasons why but it doesn't really matter)

...but it's complicated and it shouldn't be! We write Rust so that we can avoid the horrible pitfalls of C most of the times...using the standard C library directly defeats the purpose of this :)

The problem really is that println!() fails to get hold of stdout and it fails.

But there is an alternative, use writeln!(), which returns a Result<T> instead of panicking!
This makes the "ignore write error" behaviour more explicit, for example if you print using writeln!() like this:

// note that `writeln!()` uses the `std::io::Write` trait which has to be in scope
writeln!(std::io::stdout(), "{}...", whatever);

Rust would warn you that writeln!() may fail, it returns a Result and the potential error should be handled explicitly.
If you just unwrap() you get roughly the same behaviour as before (panic) but in this case you could use unwrap_or_default() to ignore the error and carry on.

In other words replace the println! in main.rs with writeln!(std::io::stderr(), [...] should solve the issue (unless I'm misunderstanding this, which is possible of course) without having to rely on conditional compilation, foreign functions, unstable, the standard C library being present and what not :) (which has the added benefit of possibly solving this problem on any non-unix platform)

Don't know if any of this makes sense :)

[jnioche]

Clippy doesn't like it
https://rust-lang.github.io/rust-clippy/master/index.html#explicit_write

We'll tell it to shut up

[xoen]

Possibly worthy adding a note to the CHANGELOG for this?

### Fixed

- [...]
- prevent CLI to panic when the pipe is broken ([issue #5](https://github.com/jnioche/carbonintensity-api/issues/5))

[xoen]

🎉