- added new `org.openpreservation.odf.validation.Rule` interface for extended checks;
- implemented `org.openpreservation.odf.validation.AbstractRule` class;
- implemented `ODF_2` compliance test and reporting;
- added `org.openpreservation.odf.validation.Rules` utility class; and
- tidied `PackageParserTest` class.

- implemented package `mimetype` entry detection as `ODF_3` rule;
- added null archive protection for `org.openpreservation.odf.pkg.OdfPackageImpl` methods; and
- added `Rules` method to get `ODF_3`rule.

- implemented rule for extension and MIME type checking;
- added `Rules` method for instantiation of rule; and
- cleaned up unnecessary exceptions.

- added necessary Package methods to implement digital signature detection;
- implemented digital signature detection for ODF_9 in `DigitalSignaturesRule`; and
- added method to `Rules` for easy rule instantiation.

- swapped `MAN-1` and `MAN-4` so that the first matches the reporting in the spec.