Remove early documentation from the repo

[HadrienGardeur]

While this was initially meant to be a monorepo hosting the Readium Web project, things shifted to a different approach a while back.

The Readium Web project is now split in two between the TypeScript and Go toolkits but this repo still contains documentation of what it was before in its early days.

We need to remove these documents from the repo and once that's done, I'm also in favor of merging back the dev branch into main. We're sending the wrong signal when people check this repo and see that the last commit was several years ago.