* Move params validation to corresponding class: We only need to valide the
params when they need to be set / are actually used. Since Puppet 4.6 or 4.7,
stdlib's validate_string function doesn't accept undef anymore, so this has
to be changed.

* Remove specific error checking in specs: types checking validate_* functions
have different error messages depending on the version the stdlib module, the
version of puppet, maybe the version of ruby, the phase of the Moon... who knows.

The postmap command needs the complete path of the database

* Add a map define to create postfix maps

It is similar to existing hash define, but this define can create maps
of any type, not just hash.

* Refactor postfix::hash to avoid duplicate code

postfix::hash uses now the new postfix::map to create the hash

May address #130

- Should only install on Debian based OS Family
- Should not install on RedHat based OS Family

Fix #75 and #85

Test with puppet parser validate and puppet-lint.
http://docs.puppetlabs.com/guides/style_guide.html

Based on a suggestion and patch from Nick Anderson. Thanks !

find . -type f -exec perl -pi -e 's/postfix-ng/postfix/' {} \;