Presentation makefile: split different operations.

docs/pres/makefile

@@ -1,5 +1,10 @@
-all:
-	-rm ./*.txt 2>/dev/null || true
-	cat ../libipc.md | md2point
-	catpoint *.txt
+all: clean generate display
 
+clean:
+	-rm ./*.txt 2>/dev/null || true
+
+generate:
+	cat ../libipc.md | md2point
+
+display:
+	catpoint *.txt