Added support for creating Manifest objects manually.  Implemented some additional methods to make this a bit less tedious.
Added error-handling when creating manifest entries to prevent an exception when passing a null value for the root directory.  Also commented out (currently) unused progress completion variables.  They likely weren't in the compiled output, but if it means that Resharper will complain less, I'm on board with that.
Changed visibility on a number of event handlers on the ManifestValidator class.  Presumably I left these as "protected" so that they could be overridden in inheriting classes, but I see very little benefit from doing so.  (The entire class needs to be abstracted on a more granular level, in my opinion).
Added XMLDOC comments to the ManifestValidatorResult class.
Modified the sample program to include examples for creating manifest files automatically as well as manually.  This needs better documentation (in the form of comments, as I expect developers to be the target audience.)