WIP, appending strings during typing or after last string finished

[mattboldt]

Requirements

• [ ] Have you viewed your changes locally on the demos page, located on https://github.com/mattboldt/typed.js/blob/master/index.html?

• [ ] If necessary, have you added a new demo to the index.html list of demos? If it's an improvement or small addition, have you added it to an existing demo on the demos page?

• [ ] If applicable, have you created a fork of the following JSFiddle with your branch's code and your new feature showcased?

Description of the Change

Benefits

Issues

[krannnn]

Hey @mattboldt, is this ready? if not when do you think this can be used?