Add RecordType (for ogg support, future known types), read Steam dir from registry

Though it looks like I changed the whole Program.cs, I just added a RecordType enum for known record types (currently just xml, png and ogg) and set it when reading inside the Record base class.  Then when we write the record out to a file, I use this record type as the file extension.  This ensures ogg files (video and audio) are written out with the correct extensions, and leaves a hook for future work.  I also made it read the location of the steam dir on windows from the registry.