ci: Migrate CI from Azure Pipelines to GitHub Actions (#233)

Migrated CI from Azure Pipelines to GitHub Actions.
Until the release process is figured out in Actions, we'll stick to using Azure pipelines for releases.

.github/workflows/continuous-integration.yml

@@ -0,0 +1,93 @@
+name: Continuous Integration
+on: push
+jobs:
+  # Run the `rustfmt` code formatter
+  rustfmt:
+    name: Rustfmt [Formatter]
+    runs-on: ubuntu-latest
+    steps:
+      - uses: hecrj/setup-rust-action@master
+      - uses: actions/checkout@master
+      - name: Install rustfmt
+        run: rustup component add rustfmt
+      - name: Run rustfmt
+        run: cargo fmt --all -- --check
+
+  # Run the `clippy` linting tool
+  clippy:
+    name: Clippy [Linter]
+    runs-on: ubuntu-latest
+    steps:
+      - uses: hecrj/setup-rust-action@master
+      - uses: actions/checkout@master
+      - name: Install clippy
+        run: rustup component add clippy
+      - name: Run clippy
+        run: cargo clippy --all-targets --all-features -- -D clippy::all
+
+  # Ensure that the project could be successfully compiled
+  cargo_check:
+    name: Compile
+    runs-on: ubuntu-latest
+    steps:
+      - uses: hecrj/setup-rust-action@master
+      - uses: actions/checkout@master
+      - run: cargo check --all
+
+  # Run tests on Linux, and macOS
+  # On both Rust stable and Rust nightly
+  test:
+    name: Test Suite
+    needs: [rustfmt, clippy, cargo_check]
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macOS-latest]
+        rust: [stable, nightly]
+    steps:
+      # Install all the required dependencies for testing
+      - uses: hecrj/setup-rust-action@master
+        with:
+          rust-version: ${{ matrix.rust }}
+
+      # Install Node.js at a fixed version
+      - uses: actions/setup-node@master
+        with:
+          node-version: "12.0.0"
+
+      # Install Golang at a fixed version
+      - uses: actions/setup-go@master
+        with:
+          go-version: "1.12.1"
+
+      # Install Ruby at a fixed version
+      - uses: actions/setup-ruby@master
+        with:
+          ruby-version: "2.6.3"
+
+      # Install Python at a fixed version
+      - uses: actions/setup-python@master
+        with:
+          python-version: "3.6.9"
+
+      # Run the ignored tests that expect the above setup
+      - uses: actions/checkout@master
+      - name: Run all tests
+        run: cargo test  -- -Z unstable-options --include-ignored
+
+  # Run the tests in the Docker image
+  docker_test:
+    name: Test in Docker
+    needs: [rustfmt, clippy, cargo_check]
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@master
+      - name: Pull the pre-built Docker image
+        run: docker pull starshipcommand/starship-test
+      - name: Fix file permissions
+        run: chmod -R a+w .
+      - name: Build the Docker image
+        run: docker build -f tests/Dockerfile --tag starshipcommand/starship-test --cache-from starshipcommand/starship-test .
+      - name: Run tests in Docker
+        run: docker run --rm -v $(pwd):/src/starship starshipcommand/starship-test