Allow forwarding benchmark's stdout to hyperfine

This change makes it possible to forward the stdout of the command the
user tries to benchmark to hyperfine's stdout using the `--print-stdout`
flag.

This should be irrelevant for most use-cases, however it makes it
possible to get some crude benchmarks of terminal emulators similar to
what's currently often done with `time cat file`.

src/main.rs

@@ -56,7 +56,8 @@ pub fn error(message: &str) -> ! {
 
 /// Runs the benchmark for the given commands
 fn run(commands: &Vec<Command>, options: &HyperfineOptions) -> io::Result<Vec<BenchmarkResult>> {
-    let shell_spawning_time = mean_shell_spawning_time(&options.output_style)?;
+    let shell_spawning_time =
+        mean_shell_spawning_time(&options.output_style, options.print_stdout)?;
 
     let mut timing_results = vec![];
 
@@ -128,11 +129,13 @@ fn build_hyperfine_options(matches: &ArgMatches) -> HyperfineOptions {
 
     options.preparation_command = matches.value_of("prepare").map(String::from);
 
+    options.print_stdout = matches.is_present("print-stdout");
+
     options.output_style = match matches.value_of("style") {
         Some("full") => OutputStyleOption::Full,
         Some("basic") => OutputStyleOption::Basic,
         Some("nocolor") => OutputStyleOption::NoColor,
-        _ => if atty::is(Stream::Stdout) {
+        _ => if !options.print_stdout && atty::is(Stream::Stdout) {
             OutputStyleOption::Full
         } else {
             OutputStyleOption::Basic