JS Browser support

Just wanted to let you know the content hasher works nicely in the browser with a small change to the packages being used:

```diff
- const crypto = require('crypto')
+ import { Buffer } from 'buffer/'
+ import crypto from 'crypto-browserify'
```

Packages:

```
npm install buffer
npm install crypto-browserify
```

That's all I had to change for my Webpack-based app.

The issue does not name a repository file or test. Start by locating the content hasher's current crypto require and checking its package dependencies and Webpack browser build; verify the documented buffer and crypto-browserify setup works in a browser-based app. Done means the content hasher can be bundled and used in the browser without the reported change being applied manually.

Written by the indexing model from the issue text.