Added atob and btoa for node

snippets/btoa.md

@@ -0,0 +1,13 @@
+### btoa
+
+Creates a base-64 encoded ASCII string from a String object in which each character in the string is treated as a byte of binary data.
+
+Create a `Buffer` for the given string with binary encoding and use `Buffer.toString('base64')` to return the encoded string.
+
+```js
+const btoa = str => new Buffer(str, 'binary').toString('base64');
+```
+
+```js
+btoa('foobar'); // 'Zm9vYmFy'
+```