Auto register side effects and Update documentation (#872)

* Update chai/{testing-style} to chai/register-{testing-style}

* Update documentation on registering side effects and remove module.exports

* Update README.md usage for minor consistency issues

README.md

@@ -107,35 +107,54 @@ You can also use it within the browser; install via npm and use the `chai.js` fi
 Import the library in your code, and then pick one of the styles you'd like to use - either `assert`, `expect` or `should`:
 
 ```js
-var chai = require('chai');
-// Using Assert style
-var assert = chai.assert;
-// Using Expect style
-var expect = chai.expect;
-// Using Should style
-var should = chai.should();
+var chai = require('chai');  
+var assert = chai.assert;    // Using Assert style
+var expect = chai.expect;    // Using Expect style
+var should = chai.should();  // Using Should style
 ```
 
-## Native Modules Usage
+### Pre-Native Modules Usage (_registers the chai testing style globally_)
 
 ```js
-import assert from 'chai/assert'
-// Using Assert style
-import expect from 'chai/expect'
-// Using Expect style
-import should from 'chai/should'
-// Using Should style
+require('chai/register-assert');  // Using Assert style
+require('chai/register-expect');  // Using Expect style
+require('chai/register-should');  // Using Should style
 ```
 
-## Usage with Mocha
+### Pre-Native Modules Usage (_as local variables_)
+
+```js
+const { assert } = require('chai');  // Using Assert style
+const { expect } = require('chai');  // Using Expect style
+const { should } = require('chai');  // Using Should style
+should();  // Modifies `Object.prototype`
+
+const { expect, use } = require('chai');  // Creates local variables `expect` and `use`; useful for plugin use
+```
+
+### Native Modules Usage (_registers the chai testing style globally_)
+
+```js
+import 'chai/register-assert';  // Using Assert style
+import 'chai/register-expect';  // Using Expect style
+import 'chai/register-should';  // Using Should style
+```
+
+### Native Modules Usage (_local import only_)
+
+```js
+import { assert } from 'chai';  // Using Assert style
+import { expect } from 'chai';  // Using Expect style
+import { should } from 'chai';  // Using Should style
+should();  // Modifies `Object.prototype`
+```
+
+### Usage with Mocha
 
 ```bash
-mocha spec.js -r chai/assert # OR:
-# Using Assert style
-mocha spec.js -r chai/expect # OR:
-# Using Expect style
-mocha spec.js -r chai/should
-# Using Should style
+mocha spec.js -r chai/register-assert  # Using Assert style
+mocha spec.js -r chai/register-expect  # Using Expect style
+mocha spec.js -r chai/register-should  # Using Should style
 ```
 
 [Read more about these styles in our docs](http://chaijs.com/guide/styles/).

register-assert.js

@@ -0,0 +1 @@
+global.assert = require('./').assert;

register-expect.js

@@ -0,0 +1 @@
+global.expect = require('./').expect;

register-should.js

@@ -0,0 +1 @@
+global.should = require('./').should();