printf: include missing header files

string, cctype and cstdint were missing
menu.impl.hpp: include numeric instead of algorithm
error.cpp: braces around return string

fixes build bug with libcxx (IMHO a bug in libcxx)
item: added two new function based name models

both models have a std::function, which gets a const item& and which
is called by get_name and get_desc.
function_name_model, which directly returns a const char*,
fun_str_name_model returns a std::string, which is additionaly stored in
the name_model
interface: use str_fun_name_model for item
error.hpp: include missing string header

fixes build error with libcxx
tiny README update
build with libc++
list chars by initiative value
move initiative to own header + source file
initiative: add conversion from string
menu.impl: added missing algorithm header