build: CMake API parameter values handling and documentation improved

Relates to #581

src/CMakeLists.txt

@@ -85,7 +85,7 @@ check_cxx_feature_supported(__cpp_explicit_this_parameter ${projectPrefix}EXPLIC
 
 # validate settings
 if(NOT ${projectPrefix}API_FREESTANDING
-   AND ${projectPrefix}API_STD_FORMAT STREQUAL "TRUE"
+   AND "${projectPrefix}API_STD_FORMAT"
    AND NOT
        (${projectPrefix}LIB_FORMAT_SUPPORTED
         # libc++ has a basic supports for std::format but does not set __cpp_lib_format
@@ -96,13 +96,11 @@ if(NOT ${projectPrefix}API_FREESTANDING
     message(FATAL_ERROR "`std::format` enabled but not supported")
 endif()
 
-if(${projectPrefix}API_STRING_VIEW_RET STREQUAL "TRUE" AND NOT
-                                                           ${projectPrefix}STATIC_CONSTEXPR_VARS_IN_CONSTEXPR_FUNCTIONS
-)
+if("${projectPrefix}API_STRING_VIEW_RET" AND NOT ${projectPrefix}STATIC_CONSTEXPR_VARS_IN_CONSTEXPR_FUNCTIONS)
     message(FATAL_ERROR "`std::string_view` returns enabled but not supported")
 endif()
 
-if(${projectPrefix}API_NO_CRTP STREQUAL "TRUE" AND NOT ${projectPrefix}EXPLICIT_THIS_PARAMETER_SUPPORTED)
+if("${projectPrefix}API_NO_CRTP" AND NOT ${projectPrefix}EXPLICIT_THIS_PARAMETER_SUPPORTED)
     message(FATAL_ERROR "`NO_CRTP` mode enabled but explicit `this` parameter is not supported")
 endif()