Host documentation for multiple verisons of the library

At the moment we host only the documentation for the latest released version of the library. However, this means that when we've released a beta with breaking changes, the documentation only covers a version of the library that most users won't ever see. Instead, we should change the organization of the documentation so that we have /latest/ and /stable/ versions of the documentation, while also making the docs for each released version available using a corresponding path (e.g. /0.8.0/).

Note that this will require rather major changes to our release pipeline since it's quite different from how we do things now.