SPECFEM3D v4.0.0

New in SPECFEM3D 4.0.0:

• various code improvements (fault solver, FK/DSM/AxiSEM coupling, gravity perturbations, energy integrals)
• inverse problem module
• parallel heuristic mesh decomposer
• ADIOS2 file I/O support
• ASDF seismogram output
• HIP GPU support

many thanks for all your contributions to this version:
Rafael Almada, Jean-Paul Ampuero, Etienne Bachmann, Kangchen Bai, Stephen Beller, Jordan Bishop, Alexis Bottero, Emanuele Casarotti, Clement Durochat, Rene Gassmoeller, Hom Nath Gharti, Leopold Grinberg, Aakash Gupta, Foivos Karakostas, Dimitri Komatitsch, Qinya Liu, Geordie McBain, Ryan Modrak, Vadim Monteiller, Masaru Nagaso, Elif Oral, Daniel Peter, Elliott Sales de Andrade, James Smith, Carl Tape, Eduardo Valero Cano, Huihui Weng, Zhinan Xie