'make class' target - make all PDFs and put them in one place

Makefile

 SUBDIRS=syllabus schedule assignments lectures
 
 include Makerules
+
+#
+# Build all PDFs for the class and collect them in one directory
+#
+.PHONY: class
+
+class: all
+	-rm -rf class/
+	mkdir class/
+	./makeclass
+