build(docs): do not run docs Makefile target if no changes in docs/so…

…urce; remove the check and test dependencies from the docs target (#560)

Makefile

@@ -188,21 +188,24 @@ dist/$(PACKAGE_NAME)-$(PACKAGE_VERSION)-build-epoch.txt:
 	echo $(SOURCE_DATE_EPOCH) > dist/$(PACKAGE_NAME)-$(PACKAGE_VERSION)-build-epoch.txt
 
 # Build the HTML and Markdown documentation from the package's source.
+DOCS_SOURCE := $(shell git ls-files docs/source)
 .PHONY: docs docs-html docs-md
 docs: docs-html docs-md
-docs-html: docs/_build/html/index.html
-docs/_build/html/index.html: check test
+docs-html: docs/_build/.html-built-on
+docs/_build/.html-built-on: $(DOCS_SOURCE)
 	if [ ! -d docs/source/_static ]; then \
 	  mkdir docs/source/_static/; \
 	fi
 	$(MAKE) -C docs/ html
-docs-md: docs/_build/markdown/Home.md
-docs/_build/markdown/Home.md: check test
+	echo "Automatically generated by Python Package Makefile on $$(date '+%Y-%m-%d %H:%M:%S %z')." > docs/_build/.html-built-on
+docs-md: docs/_build/.markdown-built-on
+docs/_build/.markdown-built-on: $(DOCS_SOURCE)
 	if [ ! -d docs/source/_static ]; then \
 	  mkdir docs/source/_static/; \
 	fi
 	$(MAKE) -C docs/ markdown
 	mv docs/_build/markdown/index.md docs/_build/markdown/Home.md
+	echo "Automatically generated by Python Package Makefile on $$(date '+%Y-%m-%d %H:%M:%S %z')." > docs/_build/.markdown-built-on
 
 # Prune the packages currently installed in the virtual environment down to the required
 # packages only. Pruning works in a roundabout way, where we first generate the wheels for