Add github actions.

[philderbeast]

Adds github actions for cabal and stack (lts-18.14) for ghc-8.10.7. Removed regex-compat-tdfa and json from extra-deps as they're included with lts-18.14. Opted not to mess with ./stack.yaml at lts-18.8 for ghc-8.10.4 as it has commentary I didn't want to mess with. The stack runner yaml configuration uses ./stack/stack-8.10.7.yaml.

I've seen test failures but that is a separate issue #212.

The ci runners are triggered on:

on:
  push:
    branches: [ci-cabal, add/github-actions]
  pull_request:
    branches: [master]

Later we could remove add/github-actions from the push branches list but for now it is useful for triggering both stack and cabal runners.