Fix some Version class problems
Fix some Version class problems

- Print 0 if build and/or revision wasn't initialized by the user
- Add a CompareTo(Version,Version) method to compare versions, treating
  undefined values as 0.

0xd4d/dnlib,modulexcite/dnlib,ZixiangBoy/dnlib,ilkerhalil/dnlib,jorik041/dnlib,Arthur2e5/dnlib,yck1509/dnlib,kiootic/dnlib,picrap/dnlib