The motivation for this change is:
* To catch build failures in downstream packages whenever we make a breaking
change to the `dhall` API
* To reduce the amount of work I need in order to cut a release for all of
these packages
* To better share Nix/CI-related logic between the projects
Note that I have not yet migrated `dhall-nix` in. I'm waiting for
https://github.com/dhall-lang/dhall-nix/issues/17 to be fixed since
`dhall-nix` is incompatible with later versions of `megaparsec` due to
`hnix`.
Fixes https://github.com/dhall-lang/dhall-haskell/issues/645
Fixes https://github.com/dhall-lang/dhall-lang/issues/216
This updates the `README` with the following changes:
* Points to the language-agnostic `README` in the `dhall-lang` repository
* Retains only Haskell-specific sections of interest
* Removes the embedded LICENSE now that GitHub auto-recognizes the project
license (#644)
* Changes the Quick Start instructions to use Nix
* Adds instructions for project development using Nix
The latter two points entailed refactors to the Nix logic to simplify the
user experience:
* `default.nix` was moved to `shared.nix` and replaced with a new `default.nix`
that works out-of-the-box with `nix-build`
* There is a new `nix/test-dhall.nix` which users can use to create a
`nix-shell` with Dhall as a dependency
