Update Makefile

docs/Makefile

@@ -1,12 +1,12 @@
 # Minimal makefile for Sphinx documentation
 #
+SUBDIRS = source/man
 
-# You can set these variables from the command line, and also
-# from the environment for the first two.
-SPHINXOPTS    ?=
-SPHINXBUILD   ?= sphinx-build
+# You can set these variables from the command line.
+SPHINXOPTS    += -W
+SPHINXBUILD   = sphinx-build
 SOURCEDIR     = source
-BUILDDIR      = build
+BUILDDIR      = _build
 
 # Put it first so that "make" without argument is like "make help".
 help:
@@ -17,4 +17,5 @@ help:
 # Catch-all target: route all unknown targets to Sphinx using the new
 # "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
 %: Makefile
+	@for dir in source/man source/*-man; do $(MAKE) -C $$dir; done
 	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)