Modernize CMakeLists.txt for inifile-cpp

[abin-z]

Modernize CMakeLists.txt for inifile-cpp

This PR updates the CMakeLists.txt to a more modern, target-oriented CMake style while keeping the previous functionality intact.

Main changes

1. Modern CMake targets

   • inicpp is now an INTERFACE library with proper target_compile_features.
   • Compiler options and include paths are applied per target instead of globally.

2. C++ standard

   • Explicit cxx_std_11 declared via target_compile_features.
   • Removes global CMake variables (CMAKE_CXX_STANDARD) for cleaner builds.

3. Option naming

   • All options prefixed with INIFILE_CPP_ to avoid global conflicts:
     • INIFILE_CPP_GENERATE_COVERAGE
     • INIFILE_CPP_BUILD_TESTS
     • INIFILE_CPP_BUILD_EXAMPLES

4. Coverage

   • Enabled only for master project and GCC/Clang.
   • Message displayed when coverage is enabled.
   • Avoids polluting downstream targets when the library is used via add_subdirectory.

5. Tests and examples

   • Conditional inclusion only when master project.
   • Clear build messages to inform user.

6. Install

   • Uses GNUInstallDirs for portable installation paths.
   • Installs all header files in include/ directory rather than a single file.

Benefits

• Fully Modern CMake and target-oriented
• Cleaner and safer build system
• Better separation between library, tests, and examples
• Easier to maintain and extend for future development

Modern CMake: https://cliutils.gitlab.io/modern-cmake/README.html

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.40%. Comparing base (7e49789) to head (27e0df2).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #48      +/-   ##
==========================================
- Coverage   93.84%   93.40%   -0.44%     
==========================================
  Files           1        1              
  Lines         341      288      -53     
==========================================
- Hits          320      269      -51     
+ Misses         21       19       -2     

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