Support C++ Modules

[kaladron]

Hi! I wrote a small wrapper for tabulate for C++ Modules that I'd be happy to contribute upstream if you're interested:

module;

#include <tabulate/table.hpp>

export module tabulate;

export namespace tabulate {
using tabulate::Table;
using tabulate::FontAlign;
using tabulate::FontStyle;
}  // namespace tabulate

(used in my code today as: https://raw.githubusercontent.com/kaladron/galactic-bloodshed/refs/heads/main/gb/third_party/tabulate.cppm)

If yes, i'll happily put together the PR that links this into cmake, etc.