Add basic benchmark

This is based on a one-off benchmark from #13

Cargo.toml

@@ -26,3 +26,10 @@ travis-ci = { repository = "unicode-rs/unicode-xid" }
 default = []
 no_std = []
 bench = []
+
+[dev-dependencies]
+criterion = "0.3"
+
+[[bench]]
+name = "xid"
+harness = false

benches/xid.rs

@@ -0,0 +1,60 @@
+extern crate criterion;
+extern crate unicode_xid;
+
+use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion, Throughput};
+use unicode_xid::UnicodeXID;
+
+fn bench_unicode_xid(c: &mut Criterion) {
+    let unicode_chars = chars(1..0x3000);
+    let ascii_chars = chars(1..0x80);
+
+    let mut group = c.benchmark_group("UnicodeXID");
+    group.throughput(Throughput::Bytes(unicode_chars.len() as u64));
+    group.bench_with_input(
+        BenchmarkId::new("is_xid_start", "unicode"),
+        &unicode_chars,
+        |b, chars| b.iter(|| chars.iter().copied().map(UnicodeXID::is_xid_start).last()),
+    );
+    group.throughput(Throughput::Bytes(ascii_chars.len() as u64));
+    group.bench_with_input(
+        BenchmarkId::new("is_xid_start", "ascii"),
+        &ascii_chars,
+        |b, chars| b.iter(|| chars.iter().copied().map(UnicodeXID::is_xid_start).last()),
+    );
+    group.throughput(Throughput::Bytes(unicode_chars.len() as u64));
+    group.bench_with_input(
+        BenchmarkId::new("is_xid_continue", "unicode"),
+        &unicode_chars,
+        |b, chars| {
+            b.iter(|| {
+                chars
+                    .iter()
+                    .copied()
+                    .map(UnicodeXID::is_xid_continue)
+                    .last()
+            })
+        },
+    );
+    group.throughput(Throughput::Bytes(ascii_chars.len() as u64));
+    group.bench_with_input(
+        BenchmarkId::new("is_xid_continue", "ascii"),
+        &ascii_chars,
+        |b, chars| {
+            b.iter(|| {
+                chars
+                    .iter()
+                    .copied()
+                    .map(UnicodeXID::is_xid_continue)
+                    .last()
+            })
+        },
+    );
+    group.finish();
+}
+
+fn chars(range: std::ops::Range<u32>) -> Vec<char> {
+    range.filter_map(|i| std::char::from_u32(i)).collect()
+}
+
+criterion_group!(benches, bench_unicode_xid);
+criterion_main!(benches);