Add benchmarking code for json parser

benches/json-benchmark.rs

@@ -1,8 +1,13 @@
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
-use tests::json_parser::json_object;
+use parser_combinator::testutil::json_object;
+use parser_combinator::Parser;
 
 pub fn criterion_benchmark(c: &mut Criterion) {
-    c.bench_function("fib 20", |b| b.iter(|| fibonacci(black_box(20))));
+    let test_json = include_str!("../tests/joplin-cfg.json");
+
+    c.bench_function("parse_json", |b| {
+        b.iter(|| json_object().parse(black_box(test_json)))
+    });
 }
 
 criterion_group!(benches, criterion_benchmark);