When profiling the GPU version, NVTX can be used to highlight the
corresponding regions of the code in the timeline of the profiling tool
(nvvp or nsight systems). This is very useful to correlate what happens
on the GPU with what part of the code we are in.

On heterogenous cluster, of nodes with different CPUs the _experimental_
feature (--enable-heterogenous-cluster-support) can be used:

It compares the (Intel) cpuid set of all CPUs which are used by ELPA MPI
processes and finds the SIMD instruction set, which is supported by all
used CPUs. The ELPA 2stage back-transformation kernel (a.k.a "kernel")
will be set accordingly on all MPI processes.

This feature, can override the setting of the kernel done previously by
the user!

At the moment it will only work for Intel CPUs, i.e. clusters consisting
of nodes with Intel CPUs and e.g. AMD CPUs are at the moment _NOT_
supported.

Since this is an experimental feature, it might be dropped again in the
future, if it turns out not to be useful for the users

- remove deprecated features
- update ABI and API versioning

- updated INSTALL
- change the ELPA vesioning number
- update Changelog and RELEASE_NOTES

Still to do:
- ABI versioning
- API version number
- Release notes
- Changelog
- Issues
- remove deprecated features
- update of API documentation

also introducing --with-likwid parameter to the configure script

Can be used to compile with likwid and to enable the likwid to measure
performance of individual compute steps

with AC_COMPILE_IFELSE in the configure.ac script

Add parts to configure.ac and Makefile.am. There is now an additional
flag --enable-python-tests. The tests require the pytest package.

The implementation of the test is a bit hacky because it takes
wrapper.so from .libs. This should probably improbed for better
portability.

By default, python wrapper is not built, only if this switch is
specified.

- depends on python, cython, mpi4py and numpy
- currently only dependency check on python
- should be done optionally
- converts wrapper.pyx to wrapper.c using cython, then compiles this to
  a python extension
- installs the files such that they can be imported with `import pyelpa`
  in python