build: add directory-oriented make workflows

docs/Makefile

@@ -1,12 +1,38 @@
-MDBOOK ?= mdbook
+override SHELL := /bin/sh
+override MAKEFLAGS += --no-print-directory
 
-.PHONY: build serve test
+.DEFAULT_GOAL := help
+.DELETE_ON_ERROR:
 
-build:
+override MDBOOK := mdbook
+
+override PRIMARY_GOAL := $(firstword $(MAKECMDGOALS))
+
+ifeq ($(PRIMARY_GOAL),run)
+
+.PHONY: run
+
+# Application arguments may also look like Make goals. The run recipe recovers
+# their exact boundaries from the original invocation.
+.DEFAULT:
+	@:
+
+else
+
+.PHONY: help run check
+
+help:
+	@printf '%s\n' 'Usage: make docs -- <mdbook arguments...>' '' \
+		'With no arguments, mdbook test and mdbook build are run.' \
+		'Example: make docs -- build' '' \
+		'Project target:' \
+		'  check  Run mdbook test and mdbook build'
+
+endif
+
+check:
+	$(MDBOOK) test
 	$(MDBOOK) build
 
-serve:
-	$(MDBOOK) serve --open
-
-test:
-	$(MDBOOK) test
+run:
+	@exec python3 ../scripts/make-argv.py exec run $(MDBOOK)