Provides optional types for TypeScript

[qrac]

Hi! I am using rehype-prism in TypeScript and it would be helpful if a type of plugin list is provided.

The editor completion works by exporting Options. No inconvenience associated with this. Please merge if you like.

Please check if the PR fulfills these requirements

• [x] Have you followed the guidelines in our Contributing document?
• [x] Have you written new tests for your core changes, as applicable?
• [x] Have you written or modified docs for your core changes, as applicable?

[Val-istar-Guo]

It's great to see someone maintain this repository with me ^_^

[Val-istar-Guo]

new version released https://github.com/Val-istar-Guo/rehype-prism/pull/13

[qrac]

Thank you!