Prep to add /etc/cron.* managment

This commit moves what was the init.pp into crontab.pp as this is more in line
with the naming convention to manage hourly, daily, weekly and monthly jobs.

A new init.pp has been created which ensures that the cron service is running.

The crontab.pp has also gained support for purging unmanaged cron entries.
Adds support for standard periodic cron jobs

This commit adds classes for the standard hourly, daily, weekly and monthly
cron jobs.
Fixed namespaceing error

Durring the move of the old init.pp into its own crontab class the fully
qualified namespace used in one variable definition was not correctly updated to
reflect this.

This commit also added a space after a comma between variables to be consistent
in style.
Add support for setting hiera_hash globaly

This commit allows $hiera_hash to be set in the man cron class. If set to true
all child classes will use hiera_hash($foo) style lookups for cron jobs.

Previously this was done on a per class basis. This still can be set per class,
although the setting of $hiera_hash to true in the cron class will take
precedence over individual classes which are set to false (default).
Updated README

The README now contains details of the classes added for daily, hourly, weekly
and monthly jobs as well as the movement of the contrab control to it's own
class.

As there have been changes adding hiera_hash functionality the example
definition has been changed to YAML.
Merge pull request #1 from george-b/cron_dirs

Cron dirs