src: add pretty print

This commit add supports to console output
and JSON output. It checks if the script
was run without echoing to a file:
```
$ node index.js
```

Then caling pretty console ouput, or when
pipe is found
```
$ node index.js > results.json
```

Resulting in a JSON output.

Author: RafaelGSS

console-output.js

@@ -0,0 +1,22 @@
+const opsSecFormatter = Intl.NumberFormat('en-US', { notation: 'compact', maximumSignificantDigits: 4})
+
+module.exports = {
+  log (str) {
+    console.log(str);
+  },
+  printResults (results) {
+    const halfScreen = process.stdout.columns / 2;
+    console.log('-'.repeat(halfScreen));
+    for (const result of results) {
+      console.log(`${result.name}`);
+      // TODO(rafaelgss): support non-operation method
+      for (const operation of result.operations) {
+        const opName = `  ${operation.name}:`;
+        const spaces = ' '.repeat(halfScreen - opName.length);
+        console.log(opName +
+        `${spaces}${opsSecFormatter.format(operation.opsSec)} (${operation.samples} samples)`);
+      }
+    }
+    console.log('-'.repeat(process.stdout.columns / 2));
+  }
+}

index.js

@@ -12,15 +12,32 @@ const piscina = new Piscina({
   maxQueue: 1,
 });
 
+let output;
+// Considering this script won't be called as a
+// child_process, stdout.isTTY should be reliable enough.
+if (process.stdout.isTTY) {
+  output = require('./console-output');
+} else {
+  output = {
+    log: () => {},
+    printResults: (results) => {
+      console.log(JSON.stringify(results, null, 2));
+    }
+  }
+}
+
 async function main() {
   const files = await fs.readdir(path.join(__dirname, './src'));
+  output.log('Running Node.js Package Benchmark...');
+  const results = [];
   for (const file of files) {
     if (file.match(/.*-benchmark\.js$/)) {
       const benchFile = path.join(__dirname, './src/', file);
       const result = await piscina.run(benchFile);
-      console.log('results', JSON.stringify(result, null, 2));
+      results.push(result);
     }
   }
+  output.printResults(results);
 }
 
 main();