CXX23 ok (fully tested) but requires a patched testthat

Author: pachadotdev

README.Rmd

@@ -33,7 +33,8 @@ cpp4r can be used as a replacement for cpp11 in existing or new packages. Think
 they are almost identical, but cpp4r has some extra features.
 
 cpp4r requires at least C++11. It is compatible with C++14, C++17, C++20, C++23 as well. The headers are written in
-a way that is compatible with all of these standards and newer features are used if the compiler supports them.
+a way that is compatible with all of these standards and newer C++ features are used if the compiler supports them withC
+C++11 as a base.
 
 After discussing some [pull requests](https://github.com/pachadotdev/cpp11/pulls/pachadotdev) with Hadley Wickham from
 Posit, it was mentioned that I should create my own fork to add the following features: