Option for outputing multiline strings

[Kazuo256]

When you try to output a toml table with

out_stream << my_toml_table;

All string values are invariably written with a single-line quotation.

Would it be possible to add options to force writing multiline strings?

I know it is possible to do it manually using the accept method, but it would be nice to have a built-in feature.

I'm also available for submitting a PRs if you tell me how you want it done.