* Add additional SMT solvers to Docker image.
This change downloads specific stable release versions of each supported SMT solver to the Dockerfile. In cases where a build was available(yices, cvc4, Mathsat), it is downloaded directly. In other cases, it is build from a specific source snapshot (boolector, abc). These versions could be changes if desired.
This allows easy access to Cryptol and all solvers in a single Docker container, which is useful since some common problems are not amenable to solution with Z3 alone.
As with the original Cryptol Dockerfile, this implementation uses Docker's staged build functionality both to keep the final size as small as possible and to modularize the build. If desired, this segment could be copied verbatim to the SAW Dockerfile to add additional solvers there as well.
Note that this Dockerfile doesn't currently build. However, the new segment has been tested and does work. It may be desirable to update the rest of the Dockerfile before adding this change.
* Builds nightly binary tarballs on Linux, macOS, and Windows
* Runs tests on every PR and merge to master
* Includes GitHub Actions status in README instead of Travis
* Makes the GitRev recompile hack less fragile
* Makes the Makefile Cabal v3 compatible
* Builds the manual as part of the CI process
