Move all doc pages outside of directories

Avoids GitHub enforcing a trailing slash after their URLs,
which breaks "See Also" etc. links (fix #45)

.github/workflows/build-deploy.yml

@@ -3,6 +3,7 @@ name: Deploy to GitHub Pages
 on:
   push:
     branches: [master]
+  workflow_dispatch:
 
 # Sets permissions of the GITHUB_TOKEN to allow deployment to GitHub Pages
 permissions:
@@ -30,6 +31,13 @@ jobs:
         run: |
           yarn install --frozen-lockfile
           yarn build
+          for version in build/docs/{v*,master}; do
+            for f in "$version"/*/index.html; do
+              [ -e "$f" ] || continue
+              mv -v "$f" "${f%/index.html}.html"
+              rmdir --ignore-fail-on-non-empty "${f%index.html}"
+            done
+          done
       - name: Upload artifact
         uses: actions/upload-pages-artifact@v1
         with: