Split off crontab read/write to CrontabFileHandler.

This reduces bloat in the Crontab class and aids the separation of
concerns. Backwards compatibility is kept, but the old methods are
marked as deprecated.

Also added functionality to read and write Cron Jobs from arbitrary
files.

Signed-off-by: Jacob Kiers <jacob@jacobkiers.net>
Catch exception in __toString

Job::render() throws an InvalidArgumentException but __toString() is not allowed to any exception.
Removed Tests directory due to invalid case.
Re-add tests directory due to invalid case.
Merge pull request #7 from alphacomm/master

Split off crontab read/write to CrontabFileHandler and add read/write of arbitrary files.
Merge remote-tracking branch 'upstream/master'
Removed Tests directory due to invalid case.
Re-add tests directory due to invalid case.
Merge pull request #11 from timonbaetz/patch-1

Catch exception in __toString
Added unit test for toString Exception. Fixed issue.
Fix for "Undefined variable: job"
append stdout and stderr to file