v2.2

Maintenance release to support recent build environments. There are no changes to the interpreter implementation.

• Use GitHub Actions instead of Travis CI
• Add OCaml 4.08 to 4.14 to test matrix
• Update outdated documentation
• Upgrade OPAM version from 1.2 to 2.0
• Upgrade dune from 1.2 to 2.0 or later
• Upgrade base image for Docker images

v2.1

Final version for POPL 2019

v2.0

Submission to POPL AE