I'm not sure whether we should install teken as a library on any stock
FreeBSD installation, but I can imagine people want to tinker around
with it now and then. Create a /sys/teken/libteken, which holds a
Makefile to install a shared library version of the terminal emulator,
complete with a manpage.
Also add Makefiles for the demo/stress applications, to build it against
the shared library.