Use GitHub actions (#635)

* Remove travis config

* Add github workflow

.github/workflows/bookdown.yaml

@@ -0,0 +1,47 @@
+# Workflow derived from https://github.com/r-lib/actions/tree/v2/examples
+# Need help debugging build failures? Start at https://github.com/r-lib/actions#where-to-find-help
+on:
+  push:
+    branches: [main, master]
+  pull_request:
+    branches: [main, master]
+  workflow_dispatch:
+
+name: bookdown
+
+jobs:
+  bookdown:
+    runs-on: ubuntu-latest
+    # Only restrict concurrency for non-PR jobs
+    concurrency:
+      group: pkgdown-${{ github.event_name != 'pull_request' || github.run_id }}
+    env:
+      GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: r-lib/actions/setup-pandoc@v2
+
+      - uses: r-lib/actions/setup-r@v2
+        with:
+          use-public-rspm: true
+
+      - uses: r-lib/actions/setup-renv@v2
+
+      - name: Cache bookdown results
+        uses: actions/cache@v4
+        with:
+          path: _bookdown_files
+          key: bookdown-${{ hashFiles('**/*Rmd') }}
+          restore-keys: bookdown-
+
+      - name: Build site
+        run: bookdown::render_book("index.Rmd", quiet = TRUE)
+        shell: Rscript {0}
+
+      - name: Deploy to GitHub pages 🚀
+        if: github.event_name != 'pull_request'
+        uses: JamesIves/[email protected]
+        with:
+          branch: gh-pages
+          folder: _book