Changes in project management stuff

* CFLAGS, INSTALL{,_{USER,GROUP}}, PREFIXDIR nad BINDIR should really be configurable (Makefile)
* respect CPPFLAGS (Makefile, install.sh)
Changed "func()" => "func(void)"

Former denotes undefined argument list, latter - empty list. Former is a
generous source of potential portability problems (and is not
standard-conformant I believe).