feature/add multiset to Reno

[Relinquish0]

The code is hosted on this repo this branch

We can talk the details in this issue.

[ansatzX]

Very excellent method development!
Hope this new feature can bring us a bright future!

Maybe you can post the link of original article which explains the details.
Also the minimal example to test it, if your code is ready.

[liwt31]

Great! Keep up with the work!