Import kcas_data into saturn

[Sudha247]

This PR proposes to add kcas_data to saturn as a separate library as mentioned in #93, much like saturn and saturn_lockfree. This PR intends to act as a conversation starter on this matter. Thoughts on this, and ideas to do it differently are welcome.

The advantage of this is improved discoverability by consolidating all parallelism-safe structures within a single repository and streamlined maintenance processes. However, this may make it tricky to make separate package releases.

I've used the latest released version of kcas_data as the development branch uses unreleased features of kcas. This needs to be updated after a new release of kcas.

cc @polytypic @lyrm