Add Makefile.am and configure.ac

Sources used:
http://www.gnu.org/software/automake/manual/automake.html
https://www.flameeyes.eu/autotools-mythbuster/

DEFAULT_FDIR is no longer necessary because --datadir can be used instead, and
.fmt files will be put in the ${pkgdatadir}/abcm2ps directory.
Add standard GNU project files.

AUTHORS
ChangeLog (symlink to Changes)
NEWS
Add README (symlink) per GNU standards