add to_utf8_bom

tools/to_utf8_bom/README.md

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+# utf8 to utf8 with bom
+
+在UTF8文件前加上UTF-8 BOM的标志。
+
+用法：
+
+```
+find src -name \*.h -exec node tools/to_utf8_bom/index.js {} \;
+```

tools/to_utf8_bom/index.js

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+var fs = require('fs');
+var options = {encoding:"utf8"};
+
+var filename = process.argv.length > 2 ? process.argv[2] : "test.c";
+
+var content = fs.readFileSync(filename).toString();
+if(content.charCodeAt(0) === 0xfeff) {
+  console.log(filename + " is utf-8 with BOM");
+} else {
+  content = "\ufeff"+content;
+  fs.writeFileSync(filename, content, options);
+  console.log(filename + " done");
+}
+