add benchmarks for primes

lib/primes/benches/benchmark.rs

@@ -0,0 +1,14 @@
+extern crate primes;
+
+use criterion::{criterion_group, criterion_main, Criterion};
+
+use crate::primes::Primes;
+
+fn bench_primes_between_10e5_and_10e6(c: &mut Criterion) {
+    c.bench_function("primes 10e5 to 10e6", |b| {
+        b.iter(|| Primes::get_between(100_000, 1_000_000))
+    });
+}
+
+criterion_group!(benches, bench_primes_between_10e5_and_10e6);
+criterion_main!(benches);