authprogs/authprogs.py: use os.path.expanduser instead of os.environ['HO...

...ME'].

 The former falls back on the user's home dir from
 the password database when HOME is unset.
doc/authprogs.md: fixing "manpage-has-errors-from-man usr/share/man/man1/authprogs.1.gz
 275: warning: macro `..' not defined" by replacing '.' with \[char46]
setup.py: fix doc/authprogs.html generation