v0.2.1

• added diagnosticism_doomgram_clear();
• added doomgram example program (examples/doomgram/);
• clang v17 compatibility;
• removed unnecessary dependency on <stdatomic.h>;
• removed unnecessary dependencies on CLASP and cstring from CMake configuration;
• examples link only core (define_example_program() no longer links CLASP);
• added EXAMPLES.md, examples/tracing.md, and generate_doxygen.sh API documentation;
• added ev example program (examples/ev/) with markdown walkthroughs;
• added version_string example program (examples/version_string/) with markdown walkthroughs;
• expanded Doxygen documentation (doc/ topic pages, header API comments, example snippets);
• added GitHub Actions CI (.github/workflows/ci.yml);
• fixed undefined m_has_overflowed identifier in diagnosticism_doomgram_push_event_time_ns() (debug builds);
• fixed CMake install omitting <diagnosticism/version_string.hpp>;
• README.md improvements (Components, DoomGram example, related projects, EXAMPLES.md, tracing example, CMake consumer quick-start, Doxygen);
• boilerplate:
  • include-guards for all public headers;
  • STLSoft references now to https://github.com/synesissoftware/STLSoft;
  • README.md layout;
  • comment lengths;
  • CMake fixes;
  • ignores;
  • markdown file consistency;
  • trivial improvements to CI;
  • helper scripts;
  • LICENSE;