add support for generating canonical maps (Fixes #42)

Add template variables that were in debian master.cf but not redhat.

Allow having mta send mail directly.

$mydestination should allow comma separated values

Fix $root_mail_recipient to allow arrays

According to the example given in manifests/mta.pp,
$mydestination should allow '$myorigin, myapp.example.com'.
However, the regular expression didn't allow this value.

According to the documentation of Mailalias, multiple
recipients should be specified as array, however, this
modules expected $root_mail_recipient to be a string.

Refactor postfix module

addition to specs..

sort all parameters and options alphabetically. remove variable from mastercf template declaration as it served no purpose

It buys us nothing, and causes interpolation when not strictly necessary