mv HelloWorld.Java HelloWorld.java; A banch of changes to Makefile

*) mv HelloWorld.Java HelloWorld.java # capital case Java extension - doesn't build with make
Changes will not be visible to git until .git/config->ignorecase is set to false (was true)

*) A banch of changes to Makefile (see Makefile comments)
.PHONY: clean
%.class : %.java instead of Old-Fashioned suffixes 
correct way of setting .SUFFIXES