Add a benchmark for hexWrite

package.json

@@ -59,7 +59,7 @@
   },
   "scripts": {
     "perf": "browserify --debug perf/bracket-notation.js > perf/bundle.js && open perf/index.html",
-    "perf-node": "node perf/bracket-notation.js && node perf/concat.js && node perf/copy-big.js && node perf/copy.js && node perf/new-big.js && node perf/new.js && node perf/readDoubleBE.js && node perf/readFloatBE.js && node perf/readUInt32LE.js && node perf/slice.js && node perf/writeFloatBE.js",
+    "perf-node": "node perf/bracket-notation.js && node perf/concat.js && node perf/copy-big.js && node perf/copy.js && node perf/new-big.js && node perf/new.js && node perf/readDoubleBE.js && node perf/readFloatBE.js && node perf/readUInt32LE.js && node perf/slice.js && node perf/writeFloatBE.js && node perf/write-hex.js",
     "size": "browserify -r ./ | uglifyjs -c -m | gzip | wc -c",
     "standard": "standard",
     "test": "tape test/*.js test/node/*.js",

perf/write-hex.js

@@ -0,0 +1,24 @@
+const BrowserBuffer = require('../').Buffer // (this module)
+const util = require('./util')
+const suite = util.suite()
+
+const LENGTH = 4096
+const browserSubject = BrowserBuffer.alloc(LENGTH)
+const nodeSubject = Buffer.alloc(LENGTH)
+
+const charset = '0123456789abcdef'
+
+let str = ''
+
+for (let i = 0; i < LENGTH * 2; i++)
+  str += charset[Math.random() * charset.length | 0]
+
+suite
+  .add('BrowserBuffer#write(' + LENGTH + ', "hex")', function () {
+    browserSubject.write(str, 'hex')
+  })
+
+if (!process.browser) suite
+  .add('NodeBuffer#write(' + LENGTH + ', "hex")', function () {
+    nodeSubject.write(str, 'hex')
+  })