Version reading may be too restrictive

[hughbe]

Couple of things here

• We should rename signature to version in RulesHeader
• We should document the format of version to be MAJOR * 100000 + something??
• We should use >= checks instead of != checks because Outlook allows for reading versions with increments (e.g. higher minor versions)
• The format of the flags seems like the upper bytes are an index into a table of versions but this is from RE and is probably wrong