Subtypes

This library provides generic inj and proj functions to lift/inject subtypes into types containing them, or extract subtypes from other types.

It is based on snippets from compdata and inspired by generic-lens.

• IIUC it generally does the same thing as generic-lens's Data.Generics.Sum.Subtype module but it seems to work on some cases where generic-lens did not work for me
• I based the code on compdata because I succeeded in following along with its implementation
• Possibly this can all be replaced with a PR to generic-lens to make it handle more cases