The earlier Makefile assumed GNU tooling in the following ways:
1. install having a -t target directory argument.
2. make having an internal rule to make a target based only on...
ansi2text: ansi2text.o
3. man pages go to /usr/local/share/man, which is not the location
on OpenBSD
Made a note about installation, pointing out the use of the MANDIR
variable to correct the man page destination.
Added an uninstall target.
