Create separate (and use) stable version docs

Currently there is only documentation for the dev version of the package (https://docs.sciml.ai/FiniteStateProjection/dev/). However, for users, the stable version is probably more interesting, but this one does not exist (https://docs.sciml.ai/FiniteStateProjection/stable/). Generally, I think most packages build and links both versions of the docs, maybe something to consider here?