Contains classes and instances related to the description of the machine architecture.
register.Register:
      describes a machine register.
    register.Category:
      describes the category of a register.
    x64, sse2, x87, msr contain the 
      registers for the x86_64 architecture
    helpers contains 
      useful functions about registers (e.g., iterating on registers, 
      getting msr from their identification number)