add summary for Recur

[stc04003]

Things to note: 1. I didn't include any documentation. 2. I used event = 0 to determine terminal times.

[wenjie2wang]

@stc04003 Thanks for PR.

I have merged it to the master branch with some function documentation and tweaks: 34f6d19. Could you have a quick look to see if I understand them correctly?

I also added you as one of the contributors to the package. I would be glad to add you as one of the authors later if you contribute more. For minor updates, I think you may directly do it without PR. For major changes, a PR and review process would still be preferred. Thanks.