use parameters in main postgresql class

Only default params are set in postgresql::params, the rest is set
in the main class in init.pp. Throughout the module, use the params
from the main class instead of postgresql::params.

These changes are not backwards compatible as global variables
like $postgresql_version are not used anymore.
postgresql: Use dollar in class parameters assignation
postgresql: reorganize class, use stdlib's validate_* commands
Manage dependencies in postgresql's init class
Merge pull request #54 from raphink/parameters

use parameters in main postgresql class
Add variable checks to postgresql::debian and postgresql::redhat
Add $check_version parameter to postgresql
Add doc for postgresql class
Add doc and lint postgresql::user
Add doc and lint postgresql::database
Add the $user parameter to postgresql::database
Improve doc for postgresql::hba
Improve doc for postgresql::conf
Merge pull request #55 from raphink/doc

Improve documentation for some postgresql classes
Add parameters to postgresql::backup
Get rid of global variables $postgresql_backupdir and $postgresql_backupfmt
Merge pull request #56 from raphink/backup

Add parameters to postgresql::backup
postgresql::hba - typo, fixes #57