Create a more automatic makefile for org-mode trees.

Unfortunately, this seems to rebuild every source file every time so I still need to work on fixing that.

org_mode_samples/Makefile

@@ -0,0 +1,25 @@
+SHELL := bash
+.ONESHELL:
+.SHELLFLAGS := -eu -o pipefail -c
+.DELETE_ON_ERROR:
+MAKEFLAGS += --warn-undefined-variables
+MAKEFLAGS += --no-builtin-rules
+SUBDIRS := $(wildcard */.)
+OUT=out
+
+ifeq ($(origin .RECIPEPREFIX), undefined)
+  $(error This Make does not support .RECIPEPREFIX. Please use GNU Make 4.0 or later)
+endif
+.RECIPEPREFIX = >
+
+.PHONY: all
+all:
+> for dir in $(SUBDIRS); do \
+>   make -C $$dir $@; \
+> done
+
+.PHONY: clean
+clean:
+> for dir in $(SUBDIRS); do \
+>   make -C $$dir $@; \
+> done