Added GH action

There's no way that this will work on the first try

.github/workflows/main.yml

@@ -0,0 +1,87 @@
+on: [push]
+name: Build and test
+jobs:
+  build:
+    name: Build on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+    steps:
+     - name: Check out
+       uses: actions/checkout@v2
+
+     - name: Cache GHC installation
+       uses: actions/cache@v4
+       id: ghcup
+       with:
+         path: |
+           ~/.ghcup/bin/*
+           ~/.ghcup/cache/*
+           ~/.ghcup/config.yaml
+           ~/.ghcup/ghc/*
+         key: CI-ghcup
+
+     - name: Setup Haskell
+       uses: haskell/actions/setup@v2
+       if: steps.ghcup.outputs.cache-hit != 'true'
+       with:
+         enable-stack: true
+
+     - name: Cache Stackage package index
+       id: pantry
+       uses: actions/cache@v4
+       with:
+         path: ~/.stack/pantry
+         key: CI-pantry-${{ env.STACK_LTS }}
+
+     - name: Recompute Stackage package index
+       if: steps.pantry.outputs.cache-hit != 'true'
+       run: stack update
+
+     - name: Cache Haskell dependencies
+       uses: actions/cache@v3
+       with:
+         path: |
+           ~/.stack/stack.sqlite3
+           ~/.stack/snapshots
+         key: CI-testdeps--${{ env.STACK_LTS }}--${{ hashFiles('stack.yaml.lock') }}
+         restore-keys: |
+           CI-testdeps--${{ env.STACK_LTS }}--
+           CI-testdeps--
+
+     - name: Cache Haskell project buildstate
+       uses: actions/cache@v4
+       with:
+         path: .stack-work
+         key: CI-builddir--${{ env.GHC_VERSION }}
+
+     - name: Build package dependencies
+       run: |
+          stack build --no-run-tests --no-run-benchmarks --only-dependencies
+     
+     - name: Build package
+       run: |
+          stack build --no-run-tests --no-run-benchmarks
+     
+     - name: Build testing dependencies
+       run: |
+          stack build --no-run-tests --no-run-benchmarks --test --bench
+     
+     - name: Run tests
+       run: |
+          stack build --test --no-run-benchmarks
+
+     - name: Build documentation
+       run: |
+         stack haddock
+
+     - name: Check documentation
+       run: |
+         stack install doctest
+         $(stack path --local-bin)/doctest src/
+
+     - name: Deploy
+       run: |
+         stack path --local-install-root