Libtool interface number history (the "c" in [c:r:a] of
https://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html).

- 0
  Legacy interface number for all releases prior to 2014.06

- 1
  Incompatible API change. Most subroutines were converted into functions
  returning a success flag. Previously, the library called exit() on error
  conditions.

  The state of release 2014.06.001 defines this interface

- 2
  Incompatible API change. The routine for ELPA 2 real case takes an
  optional argument, defining whether QR decomposition is used or not

  The state of release 2015.02.001 defines this interface

- 3
  Incompatible API change. C Functions are added to provide an C interface.
  The subroutine "get_elpa_row_col_comms" has been converted to a function
  which returns an error code.

  The state of release 2015.02.002 defines this interface

- 4
  Incompatible API change. The Fortran versions of the library functions return
  a logical indicating success or failure. The C versions of the library functions
  return an integer {0,1} for success and failure.
  Some interface need an extra argument, specifying the number of matrix columns
  (see the documentation)