CMake Minimum Version Upgrade

The minimum required version of CMake was bumped from 3.15 to 3.16. Starting with this version, CMake supports zero padded version numbers (e.g. 23.06) allowing the removal of some buggy CMake code from GPI-Space.

Fixes

  • Changed the copyright notice in source files to the more compact SPDX standard.
  • Removed the deprecated use of std::unary_function.

Miscellaneous

  • Removed the install instructions for GPI-Space dependencies. Dependencies can directly be installed through the Spack package manager instead. The removed instructions are still available through old versions of GPI-Space on the website.