Support for uploading more than one pic [mastodon]

[fireindark707]

I found this script https://github.com/itsumonotakumi/mastodon-python-exercise-50/blob/2c78014de46bfdcc0b0d9afa03a07e49667d80fb/samples/2-3.py which indicate that more than one image can be uploaded in a post. I think this function can be added to this project.

Thanks for your work!