Tweak file comments

List the filename at the top of the comment. Add a little more detail to comment for decrypter.js. Fix up the code block formatting in the index module comment.

 /*
+ * aes.js
  *
  * This file contains an adaptation of the AES decryption algorithm
  * from the Standford Javascript Cryptography Library. That work is

-/**
- * This file contains the `Decrypter` class which manages
- * AES decryption through the `decrypt` function (which uses
- * the `AES` class for lower level decrypting) and Asynchronous
- * Streams from the `AsyncStream` class
+/*
+ * decrypter.js
+ *
+ * An asynchronous implementation of AES-128 CBC decryption with
+ * PKCS#7 padding.
  */
 
 import AES from './aes';

-/**
- * Main file for Decrypter so that we can neatly export
- * all of our functionality as one object in one file
- * and we will only have to require the top level directory
- * in this case that would look like:
- * ``` JavaScript
+/*
+ * index.js
+ *
+ * Index module to easily import the primary components of AES-128
+ * decryption. Like this:
+ *
+ * ```js
  * import {Decrypter, decrypt, AsyncStream} from './src/decrypter';
  * ```
  */