Handle broken pipe errors on stdout gracefully (#932)

Replace `println!` calls on the results paths with `writeln!` on
`io::stdout()` and propagate the `io::Error` to `main`, where
`ErrorKind::BrokenPipe` is turned into a quiet `exit(0)`. This matches
the conventional behavior of command-line tools when their output pipe
is closed early (e.g. `hyperfine ... | head -n 0`), and fixes panics in
all run-output paths: the per-benchmark header and results, the speed
comparison summary, and `-`-style exports to stdout. The warnings and
"Note" outputs to stderr are converted the same way.


---------

Co-authored-by: Mathjk <Mathjk@users.noreply.github.com>
Co-authored-by: David Peter <mail@david-peter.de>

src/export/mod.rs

@@ -1,5 +1,5 @@
 use std::fs::{File, OpenOptions};
-use std::io::Write;
+use std::io::{self, Write};
 
 mod asciidoc;
 mod csv;
@@ -18,6 +18,7 @@ use self::orgmode::OrgmodeExporter;
 
 use crate::benchmark::benchmark_result::BenchmarkResult;
 use crate::options::SortOrder;
+use crate::output::console_writeln;
 use crate::util::units::Unit;
 
 use anyhow::{Context, Result};
@@ -144,8 +145,9 @@ impl ExportManager {
                 }
                 ExportTarget::Stdout => {
                     if !intermediate {
-                        println!();
-                        println!("{}", String::from_utf8(content()?).unwrap());
+                        let mut stdout = io::stdout().lock();
+                        console_writeln!(stdout)?;
+                        console_writeln!(stdout, "{}", String::from_utf8(content()?).unwrap())?;
                     }
                 }
             }