Tests for compress method

Fixed Rotate.pm POD
The method compress now returns true or false
Added tests to check compress method invocation results

Tests are failing. One of the reasons is that the compress() is not working as the description of it says it works, some files there were rotate are not marked to be compressed for some reason.
Another problem (probably easier to fix) is that the files that will be compressed have so few data that after gziping them their file size is actually bigger than it was. Files that will be rotate should have more data into them, but this will also affect the other tests that are passing.
Or the compress method should be tests separated from other tests.
Anyway, since I creating this pull request, the decision is up to you. :-)