Fundamental design decision:

- the sizes of external and internal types are assumed to be the same.
  This leaves byte ordering aside.  While assuming this the code can be
  greatly simplified and speed increases.  Since no change violating this
  assumption is in sight this is believed to be a worthwhile optimization.

- the ABI of the backend modules is not guaranteed.  Really, not guarantee
  whatsoever.  We are enforcing this in the code.  The modules and their
  users must match.  No third-party EBL module are supported or allowed.
  The only reason there are separate modules is to not have the code for
  all architectures in all the binaries.