Add new --sort option

This adds a new `--sort` option to choose the way in which the results
in the speed comparison and the markup exports are ordered.

closes #614
closes #601

src/export/json.rs

@@ -3,6 +3,7 @@ use serde_json::to_vec_pretty;
 
 use super::Exporter;
 use crate::benchmark::benchmark_result::BenchmarkResult;
+use crate::options::SortOrder;
 use crate::util::units::Unit;
 
 use anyhow::Result;
@@ -16,7 +17,12 @@ struct HyperfineSummary<'a> {
 pub struct JsonExporter {}
 
 impl Exporter for JsonExporter {
-    fn serialize(&self, results: &[BenchmarkResult], _unit: Option<Unit>) -> Result<Vec<u8>> {
+    fn serialize(
+        &self,
+        results: &[BenchmarkResult],
+        _unit: Option<Unit>,
+        _sort_order: SortOrder,
+    ) -> Result<Vec<u8>> {
         let mut output = to_vec_pretty(&HyperfineSummary { results });
         if let Ok(ref mut content) = output {
             content.push(b'\n');