Refactor of codes in node.js

1) Add async method: `binarySearch` and `btreeSearch`.
2) Refactor of tests by putting them into `tests` folder.
3) Create several new tests in details.
4) Remove useless and reformat codes to be clear.
5) Remove useless snapshots, because they can be recreated when you run `npm run test`.

binding/nodejs/tests/utils/fetchMainVersion.js

@@ -0,0 +1,9 @@
+let node_ver = process.version
+// Because nodejs's version is something like `v8.11.3`. So we should ignore `v` first
+node_ver = node_ver.substr(1);
+// Splitted by `.`
+node_ver = node_ver.split('.');
+// Take the main version number
+node_ver = parseInt(node_ver[0]);
+
+module.exports = node_ver;