Reorganize directories (#3462)

* 🚚 move files
* 🚚 rename doc folder to docs
* 🚚 rename test folder to tests

docs/Makefile

@@ -0,0 +1,34 @@
+SRCDIR = ../single_include
+
+all: create_output
+
+##########################################################################
+# example files
+##########################################################################
+
+# where are the example cpp files
+EXAMPLES = $(wildcard examples/*.cpp)
+
+# create output from a stand-alone example file
+%.output: %.cpp
+	make $(<:.cpp=) CPPFLAGS="-I $(SRCDIR)" CXXFLAGS="-std=c++11"
+	./$(<:.cpp=) > $@
+	rm $(<:.cpp=)
+
+# compare created output with current output of the example files
+%.test: %.cpp
+	make $(<:.cpp=) CPPFLAGS="-I $(SRCDIR)" CXXFLAGS="-std=c++11"
+	./$(<:.cpp=) > $@
+	diff $@ $(<:.cpp=.output)
+	rm $(<:.cpp=) $@
+
+# create output from all stand-alone example files
+create_output: $(EXAMPLES:.cpp=.output)
+
+# check output of all stand-alone example files
+check_output: $(EXAMPLES:.cpp=.test)
+
+clean:
+	rm -fr $(EXAMPLES:.cpp=)
+	$(MAKE) clean -C docset
+	$(MAKE) clean -C mkdocs