Include project version in site documentation.

docs/Makefile

@@ -39,7 +39,8 @@ deploy:
 # Catch-all target: route all unknown targets to Sphinx using the new
 # "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
 %: Makefile
-		@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+		@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) \
+		 -D version=$(PROJECT_VERSION) -D release=$(PROJECT_VERSION) $(O)
 	mvn -f ../pom.xml site -DskipTests=true
 	mkdir -p $(BUILDDIR)/html
 	cp -r ../target/site/apidocs $(BUILDDIR)/html/apidocs