Support for RefreshUsingToken method

Recap of the changes incorporated:
1.) If you want to use the client to Authorize for multiple Companies, you can just create one instance of the client.

However, to refresh tokens for multiple companies, you could use the helper method refreshUsingToken method as shown below:

https://github.com/intuit/oauth-jsclient/blob/master/src/OAuthClient.js#L235

1.0.2

Version Release -  1.0.2

1.0.1

npm publish patch

1.0.0

Final README.md changes