This minimal implementation works and enables basic (mostly default)
CPack support to build binary packages of FLTK (RPM, TGZ, NSIS, ...).
Users need the required tools like `rpmbuild` to build a particular
type of package or installer.
Using EPM or rpmbuild directly with a provided "list" file has
been discontinued: fltk.list.in (EPM) and fltk.spec.in (RPM) have
consequently been deleted.
README.CPack.txt: basic documentation
