add a way to serialize a tuple as list of strings

[ferdymercury]

Fixes https://github.com/Dobiasd/FunctionalPlus/issues/269

[Dobiasd]

Looks good. :+1: Thanks! :heart:

There are two unused parameter errors in the CI:

/__w/FunctionalPlus/FunctionalPlus/include/fplus/show.hpp:306:40: error: unused parameter 't' [-Werror,-Wunused-parameter]
void stream(const std::tuple<Args...>& t, std::list<std::string>& sl)
                                       ^
/__w/FunctionalPlus/FunctionalPlus/include/fplus/show.hpp:306:67: error: unused parameter 'sl' [-Werror,-Wunused-parameter]
void stream(const std::tuple<Args...>& t, std::list<std::string>& sl)
                                                                  ^

If you fix them (void foo(T bar) -> void foo(T)) we're good to merge.