Makefile, docs: programmatically generate version for docs (i got tired of doing it myself)

Makefile

@@ -29,12 +29,12 @@ RUSTLIBS = --extern getopt=build/o/libgetopt.rlib \
 CFLAGS += -I$(SYSEXITS)
 
 .PHONY: all
-all: dj false fop hru intcmp mm npc rpn scrut str strcmp swab true
+all: docs dj false fop hru intcmp mm npc rpn scrut str strcmp swab true
 
 # keep build/include until bindgen(1) has stdin support
 # https://github.com/rust-lang/rust-bindgen/issues/2703
 build:
-	mkdir -p build/bin build/include build/lib build/o build/test
+	mkdir -p build/bin build/docs build/include build/lib build/o build/test
 
 .PHONY: clean
 clean:
@@ -43,7 +43,7 @@ clean:
 dist: all
 	mkdir -p $(DESTDIR)/$(PREFIX)/bin $(DESTDIR)/$(PREFIX)/share/man/man1
 	cp build/bin/* $(DESTDIR)/$(PREFIX)/bin
-	cp docs/*.1 $(DESTDIR)/$(PREFIX)/$(MANDIR)/man1
+	cp build/docs/*.1 $(DESTDIR)/$(PREFIX)/$(MANDIR)/man1
 
 .PHONY: install
 install: dist
@@ -54,6 +54,13 @@ test: build
 	tests/posix-compat.sh
 	$(RUSTC) --test src/getopt-rs/lib.rs -o build/test/getopt
 
+.PHONY: docs
+docs: docs/ build
+	for file in docs/*; do original="$$(sed -n '/^\.TH/p' <"$$file")"; \
+		title="$$(printf '%s\n' "$$original" | sed \
+		"s/X\.X\.X/$$(git describe --tags --long | cut -d'-' -f1)/g")"; \
+		sed "s/$$original/$$title/g" <"$$file" >"build/$$file"; done
+
 .PHONY: rustlibs
 rustlibs: build/o/libsysexits.rlib build/o/libgetopt.rlib \
 	build/o/libstrerror.rlib