Suggested improvements

[johnnybubonic]

Hey, I have some suggestions you may want to implement:

• Python 3 compatibility
  ** Python 2 EOLs on January 1, 2020.
  ** The 2to3 utility should fix this right up. I can submit a PR or patch, however, if you prefer.

• OpenLDAP's /etc/openldap/ldap.conf/~/.ldaprc support
  ** /etc/pam_ldap.conf is deprecated in CentOS 7 and relevant releases on other distros.
  ** Either nslcd.conf syntax should instead be used, or the ldap.conf/.ldaprc file syntax should. The benefit of the latter is they allow per-user configuration and further TLS options (such as minimum required TLS version). The advantage of the former is it's a little closer to the obsolete pam_ldap.conf syntax and allow you to contain passwords in plaintext.
  *** If the ldap.conf is used, then a new argument should be created allowing one to specify a path to the password file (the -y argument for e.g. ldapsearch) (newline characters should not be stripped from this)

If you'd like, I can offer a PR for this too.