Fix compile error on Linux and update Makefile

[kinggizzardandtheinstallationwizard]

There is a fatal error in local.c that occurs in Linux but not Darwin/MacOS (unsure if other platforms are affected) if unistd.h is not included.

I also went ahead and moved all of the parts of the Makefile that vary per end-user to a new config.mk file. Additionally I bumped terminfo to the top of the list over termcap because that has been the more common option for a very long time now.

[justwheel]

@jamesjer opened a downstream Fedora Linux RPM pull request to the package spec for zork in Fedora. I am hoping that we can work together to upstream those changes, including the use of terminfo instead of termcap, as part of a series of subsequent PRs to keep zork compiling for Linux users for generations to come.

I have not taken a close look to see how this PR differs from @jamesjer's patches yet. He also did some modernization efforts to C23.

[kinggizzardandtheinstallationwizard]

I skimmed over it a little. The modernization work looks wonderful, a lot of much-needed changes. The changes in my PR do not touch much code at all, I just added a single include and rearranged the Makefile a little.