Features:

• introduced new interface-library libClaPP_SANITIZER and removed interface-library ClaPP_OPTIONS.
• introduced new cmake-files cmake/gsl.cmake and cmake/gtest.cmake.
• GSL and gtest are now included via CMake-find_package (and not via pkg_check_modules).
• introduced CMake-alias-library libClaPP::clapp.
• added support for CMake-package-install.
• added usage-examples (see folder usage).
• changed CMake message() calls to message(STATUS).
• added more nodiscard to functions/methods if applicable.
• set CMake PROPERTY SOVERSION for target clapp to ${libClaPP_VERSION_MAJOR}.${libClaPP_VERSION_MINOR}.

Fixes:

• fixed install of missing parser_container.h*-headers.
• fixed pedantic-compiler flag-whitelist required for the GSL.