Support for multiline content

[jesusoterogomez]

This PR adds support for multiline content using feedback from issues #26 and #44

I need help to test that this covers current use cases. I have tested some notifications across one of my applications and the change seems to be fully backwards compatible, but I want to make sure that I'm not breaking anyone's app with this update.

If you would like to contribute, please follow these steps to try the latest version in your application:

git clone git@github.com:jesusoterogomez/react-notify-toast.git
cd react-notify-toast
npm link && npm run compile

# in your application
npm link react-notify-toast

# Run your app as normal and test that notifications work as expected

To test a multiline notification

// JSX content
notify.show(<span>This is a <br/>multiline</br>notification</span>);

// String
notify.show("use an insanely long string here");

[jesusoterogomez]

I am using multiline notifications for this purpose with the latest changes.

[stephenfeather]

Put into the dev cycle on friday late, the stakeholders will be testing on Monday. Thanks.