see #2: update exercises and maintains of content

exercises/7/Makefile

@@ -0,0 +1,16 @@
+#
+# Makefile
+#
+# exercise solution - chapter 7
+# modern cpp tutorial
+#
+# created by changkun at changkun.de/modern-cpp
+#
+
+all: $(patsubst %.cpp, %.out, $(wildcard *.cpp))
+
+%.out: %.cpp Makefile
+	clang++ $< -o $@ -std=c++2a -pedantic
+
+clean:
+	rm *.out