Add benchmarks for memchr::memmem:find

Results:
```
short_haystack/memchr::memmem::find
                        time:   [1671827971 instructions 1671827976 instructions 1671827981 instructions]
long_haystack/memchr::memmem::find
                        time:   [256235298 instructions 256235300 instructions 256235303 instructions]
random_haystack/memchr::memmem::find
                        time:   [3276143 instructions 3276143 instructions 3276143 instructions]

short_haystack/DynamicAvx2Searcher::search_in
                        time:   [1010100472 instructions 1010100481 instructions 1010100491 instructions]
long_haystack/DynamicAvx2Searcher::search_in
                        time:   [239679929 instructions 239679930 instructions 239679931 instructions]
random_haystack/DynamicAvx2Searcher::search_in
                        time:   [1574708 instructions 1574708 instructions 1574708 instructions]
```

Summary:
* `short_haystack`: +65% instructions for `memchr::memmem:find`
* `long_haystack`: +6% instructions for `memchr::memmem:find`
* `random_haystack`: +108% instructions for `memchr::memmem:find`

Author: marmeladema

bench/Cargo.toml

@@ -6,6 +6,7 @@ publish = false
 
 [dependencies]
 criterion = "0.3"
+memchr = "2.4"
 memmem = "0.1"
 sliceslice = { path = ".." }
 sse4-strstr = { path = "sse4-strstr", optional = true }

bench/benches/i386.rs

@@ -56,6 +56,16 @@ fn search_short_haystack<M: Measurement>(c: &mut Criterion<M>) {
         });
     });
 
+    group.bench_function("memchr::memmem::find", |b| {
+        b.iter(|| {
+            for (i, needle) in needles.iter().enumerate() {
+                for haystack in &needles[i..] {
+                    black_box(memchr::memmem::find(haystack.as_bytes(), needle.as_bytes()));
+                }
+            }
+        });
+    });
+
     #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
     {
         use sliceslice::x86::DynamicAvx2Searcher;
@@ -136,6 +146,14 @@ fn search_haystack<M: Measurement>(
         });
     });
 
+    group.bench_function("memchr::memmem::find", |b| {
+        b.iter(|| {
+            for needle in &needles {
+                black_box(memchr::memmem::find(haystack, needle.as_bytes()));
+            }
+        });
+    });
+
     #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
     {
         use sliceslice::x86::DynamicAvx2Searcher;

bench/benches/random.rs

@@ -49,6 +49,14 @@ fn search<M: Measurement>(c: &mut Criterion<M>) {
                 },
             );
 
+            group.bench_with_input(
+                BenchmarkId::new("memchr::memmem::find", parameter),
+                &size,
+                |b, _| {
+                    b.iter(|| black_box(memchr::memmem::find(haystack, needle)));
+                },
+            );
+
             #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
             {
                 use sliceslice::x86::DynamicAvx2Searcher;