Modernize CMakeLists.txt with best practices and comprehensive library support

[Copilot]

This PR completely modernizes the CMakeLists.txt file, transforming it from a basic build script into a professional, standards-compliant CMake configuration that follows current best practices for header-only libraries.

What Was Changed

Before

The original CMakeLists.txt was a minimal build script with several issues:

• Used outdated CMake 3.10 minimum version
• Only built a test executable with hardcoded compiler flags
• Used deprecated include_directories() instead of target-based approach
• Had confusing platform logic (UNIX systems got .exe extension)
• No library target or installation support
• No way for external projects to consume the library

After

The modernized CMakeLists.txt now provides:

• Modern CMake 3.15+ standards with proper project declaration
• Professional INTERFACE library target (CPPConsole::CPPConsole) for header-only library
• Target-based approach using target_include_directories() and target_compile_features()
• Comprehensive installation rules with proper header and CMake config file installation
• find_package() support allowing external projects to easily consume the library
• Optional test building via CPPCONSOLE_BUILD_TESTS option
• Cross-platform compiler support using modern generator expressions
• Proper C++17 feature requirements instead of hardcoded -std=c++17

Key Features Added

1. Header-Only Library Target

add_library(CPPConsole INTERFACE)
add_library(CPPConsole::CPPConsole ALIAS CPPConsole)
target_compile_features(CPPConsole INTERFACE cxx_std_17)

2. External Project Integration

Projects can now easily use CPPConsole:

find_package(CPPConsole REQUIRED)
target_link_libraries(your_app PRIVATE CPPConsole::CPPConsole)

3. Modern Compiler Configuration

Uses generator expressions for cross-platform compatibility:

target_compile_options(CPPConsole_test PRIVATE
    $<$<CXX_COMPILER_ID:GNU,Clang>:-Wall -Wextra -pedantic>
    $<$<CXX_COMPILER_ID:MSVC>:/W4>
)

4. Complete Installation Support

• Headers install to standard locations
• CMake config files enable find_package()
• Supports both system-wide and local installation

Additional Improvements

• Enhanced Makefile: Added cross-platform support with helpful targets like make help, make configure-lib-only
• Updated README.md: Comprehensive documentation for both simple header copying and modern CMake usage
• Better .gitignore: Added CMake build artifacts

Testing

The modernized build system has been thoroughly tested:

• ✅ Library-only builds work perfectly
• ✅ Installation creates proper file structure
• ✅ External projects can successfully find and use the library
• ✅ Cross-platform compiler flags work correctly
• ✅ Both development and distribution workflows supported

This modernization makes CPPConsole much more professional and significantly easier to integrate into modern C++ projects while maintaining backward compatibility for users who prefer the simple header-copy approach.

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