More alerts available

[pidupuis]

For now, there are only information, warnings, errors or success.

We can add for instance:

• [ ] idea, in yellow with a light bulb as icon

[tobiasBora]

Thanks a lot for this package, but I would need to have another kind of alert: question. The logo would be basically a nice question mark, and it would be particularly useful, e.g. in beamer slides to introduce the open questions that we are either willing to solve or that remain.