It is not quite clear to me why GCC complains here when
WANT_SINGLE_PRECISION_REAL is not defined, as the variables are then not
used _at all_.

Nonetheless, this again prevents build on the SuSE OBS, so fix it to
make the compiler happy

These can be used internally by

  call self%set_private(name, value)

   or

  call self%get_private(name, value)

but are not valid for the self%set()/get() routines, i.e. are not
visible to users of ELPA.

The public "solve" method has been renamed "eigenvectors" since it
computes the eigenvalues and (at least parts of) the eigenvectors

Another routine "eigenvalues" will just compute the eigenvalues

This is a bit cumbersome, as it involves yet another abstract
intermediate type, but necessary due to language limitations.

We decided not to provide this information via the key/value store, but
rather to use the ftimings module for that.

@loh will take care to implement ftimings in the new API
@amarek wants to port the legacy API so that the old global module
  variables still contain valid values

The legacy API is has been (internally) ported to use the new interface.
The intent is that users of the legacy API do not have to change their
codes.

Next step is to completely adapt the .gitlab-ci.yml file

Still missing is the compatibility layer, currently it only compiles
when configure is called with

  --disable-legacy

Also, a more general solution to parameter passing via environment
variables would be nice.

Supports multiple indexes now, to be used for non-tunable 'parameters'