readpe: Change some outputs in an attempt to make output parsing easier.

  These ouputs have been changed:
    1. Machine type
    2. Image characteristics
    3. Windows subsystem
    4. Directory names

  I also introduced a compile-time switch to keep output compatibility
  with version 0.6. To enable it, compile pev with:

  $ make CFLAGS="-DLIBPE_ENABLE_OUTPUT_COMPAT_WITH_V06"

  Please, report any inconsistencies you may find.