Allow easily share and compose Emacs Lisp package overrides

[akirak]

To build some Emacs Lisp packages in Nix, Twist requires the user to override the derivations (example). At present, the API does not allow easily sharing overrides between multiple users. Ideally, there should be a community-maintained repository for an overlay, and the user should be able to define his/her own overrides in addition to that.

This is applied to both Emacs configurations and nomake. NoMake is a framework for linting and developing Emacs Lisp packages. If a package contains a dynamic module or depends on another package that requires one, it will require an override.

Some packages also have missing dependencies (which are upstream issues), which can be workaround like this.

• [x] Provide workarounds as a separate repository, in a form of overlay.
• [x] Refine the configuration API to allow composition of overrides, if necessary. not needed after #128

[akirak]

I am currently working on https://github.com/emacs-twist/overrides to finally resolve this issue. After adding a test suite to the repository, I will close this issue.