This makes build-testing and installing the minizip/miniunzip programs
as simple as "autoreconf -if && ./configure --enable-demos && make &&
make install". Without --enable-demos, the makefile will only build
and install the library, as before. Helped by Mike Frysinger.
minizip/miniunzip were not intended to be general-purpose installed
utilities, but they can be useful from time to time as a lightweight
substitute for zip/unzip. You can also use them to quickly test that
the library installation procedure worked.
