Update documentation workflow

- Add 'workflow_dispatch' target
- Force output to use colour
- Print traceback on error
- Use parallel building

.github/workflows/builddoc.yml

@@ -1,6 +1,9 @@
-name: Build document
+name: Render documentation
 
-on: [push, pull_request]
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
 
 permissions:
   contents: read
@@ -9,6 +12,9 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
   cancel-in-progress: true
 
+env:
+  FORCE_COLOR: "1"
+
 jobs:
   build:
     runs-on: ubuntu-latest
@@ -27,11 +33,11 @@ jobs:
         python -m pip install .[docs]
     - name: Render the documentation
       run: >
-        python
-        -X dev
-        -X warn_default_encoding
-        -m sphinx
+        sphinx-build
         -M html ./doc ./build/sphinx
+        -T
         -W
+        --jobs=auto
         -n
+        -vvv
         --keep-going