Add script and cmd to test hash/checksum performance

package.json

@@ -16,9 +16,9 @@
     "node": ">=0.10.0"
   },
   "scripts": {
-    "beautify": "esbeautifier 'cache.js' 'test/**/*.js'",
+    "beautify": "esbeautifier 'cache.js' 'test/**/*.js' 'perf.js'",
     "beautify-check": "npm run beautify -- -k",
-    "eslint": "eslinter 'cache.js' 'specs/**/*.js'",
+    "eslint": "eslinter 'cache.js' 'specs/**/*.js' 'perf.js'",
     "lint": "npm run beautify && npm run eslint",
     "verify": "npm run beautify-check && npm run eslint",
     "install-hooks": "prepush install && changelogx install-hook && precommit install",
@@ -30,6 +30,7 @@
     "bump-minor": "npm run pre-v && npm version minor -m 'BLD: Release v%s' && npm run post-v",
     "bump-patch": "npm run pre-v && npm version patch -m 'BLD: Release v%s' && npm run post-v",
     "test": "npm run verify --silent && mocha -R spec test/specs",
+    "perf": "node perf.js",
     "cover": "istanbul cover test/runner.js html text-summary",
     "watch": "watch-run -i -p 'test/specs/**/*.js' istanbul cover test/runner.js html text-summary"
   },

perf.js

@@ -0,0 +1,25 @@
+var fs = require( 'fs' );
+var path = require( 'path' );
+var fileEntryCache = require( './cache.js' );
+
+
+var TEST_FILE_SIZE = 32;
+var TEST_FILE_PATH = path.resolve( __dirname, '.perf.file' );
+var RUNS = 10000;
+var LOOPS = 5;
+var TIMER_NAME = 'cache.hasFileChanged (' + TEST_FILE_SIZE + ' KB file, ' + RUNS + ' runs)';
+
+
+for (var i = 0; i < LOOPS; i++) {
+  var cache = fileEntryCache.createFromFile( '.perfcache' );
+  fs.writeFileSync( TEST_FILE_PATH, new Buffer( 1024 * TEST_FILE_SIZE ) );
+
+  console.time( TIMER_NAME );
+  for (var j = 0; j < RUNS; j++) {
+    cache.hasFileChanged( TEST_FILE_PATH );
+  }
+  console.timeEnd( TIMER_NAME );
+
+  cache.deleteCacheFile();
+  fs.unlinkSync( TEST_FILE_PATH );
+}