Wishlist of requirements towards v1 release of core libraries

[adizere]

These is a collection of requirements to fulfill for supporting the community of builders using Malachite. The scope here is for the core libraries, not the engine or other sub-systems. As we're progressing towards a stable release, accepting ideas & suggestions here:

1. Prior to each release (major, minor, optionally patch), we should have a (semi) standardized way to inform users that a release is pending and to give them a heads-up, so that they can (i) prepare for the upgrade and (ii) anticipate the effort for upgrading