Add --setup (-s) option, like --prepare but runs once per batch

Add a --setup option for the use-case of wanting to do one-off setup
before a set of benchmarks, not the once-per-test setup that --prepare
does. This is useful for the cases noted in the updated documentation.

Per the feedback on https://github.com/sharkdp/hyperfine/pull/448 this
new "--setup" option will steal the "-s" short option from
"--style" (initially this was called "--build" and used the
non-conflicting "-b").

Potential future work:

I'd prefer if this and --cleanup took N number of commands, so you
could do e.g.:

    hyperfine -L rev master,next \
        -b 'git worktree add /tmp/test-{r}'  \
        -b 'make -C /tmp/test-{r} all'  \
	'make -C /tmp/test-{r} test' \
	-c 'git worktree remove /tmp/test-{r}'

I.e. a shortcut around not providing these with &&, which makes things
a bit more readable.

But the --cleanup option doesn't do that, so let's just go with what
it's doing for consistency, so for this you'll now need to do:

    hyperfine -L rev master,next \
        -b 'git worktree add /tmp/test-{r} &&
	    make -C /tmp/test-{r} all'  \
	'make -C /tmp/test-{r} test' \
	-c 'git worktree remove /tmp/test-{r}'

tests/integration_tests.rs

@@ -70,6 +70,11 @@ impl ExecutionOrderTest {
         self
     }
 
+    fn setup(&mut self, output: &str) -> &mut Self {
+        self.arg("--setup");
+        self.command(output)
+    }
+
     fn prepare(&mut self, output: &str) -> &mut Self {
         self.arg("--prepare");
         self.command(output)
@@ -147,6 +152,22 @@ fn warmup_runs_are_executed_before_benchmarking_runs() {
         .run();
 }
 
+#[test]
+fn setup_commands_are_executed_before_each_series_of_timing_runs() {
+    ExecutionOrderTest::new()
+        .arg("--runs=2")
+        .setup("setup")
+        .command("command 1")
+        .command("command 2")
+        .expect_output("setup")
+        .expect_output("command 1")
+        .expect_output("command 1")
+        .expect_output("setup")
+        .expect_output("command 2")
+        .expect_output("command 2")
+        .run();
+}
+
 #[test]
 fn prepare_commands_are_executed_before_each_timing_run() {
     ExecutionOrderTest::new()
@@ -181,6 +202,23 @@ fn cleanup_commands_are_executed_once_after_each_benchmark() {
         .run();
 }
 
+#[test]
+fn setup_prepare_cleanup_combined() {
+    ExecutionOrderTest::new()
+        .arg("--runs=2")
+        .setup("make")
+        .prepare("make testclean")
+        .command("make test")
+        .cleanup("make clean")
+        .expect_output("make")
+        .expect_output("make testclean")
+        .expect_output("make test")
+        .expect_output("make testclean")
+        .expect_output("make test")
+        .expect_output("make clean")
+        .run();
+}
+
 #[test]
 fn single_parameter_value() {
     ExecutionOrderTest::new()