Avoid XML Declaration in serialize.

[Armiixteryx]

Hello. First I want to thank you for the work in this library, specially since XML support in Rust is not quite mature actually.

This issue is to see if it is possible to indicate yaserde to avoid serialize of XML declaration. Currently I am using some like this to remove it:

let s = yaserde::ser::to_string(&model).unwrap();
let s = s.replacen("<?xml version=\"1.0\" encoding=\"utf-8\"?>", "", 1);

I think it would be better if yaserde may handle this case so creating a new String with replacen is no longer required.

Thanks for you attention.

[MarcAntoine-Arnaud]

Hello @Armiixteryx, It's already possible to skip the xml header.

You need to use to_string_with_config method, and the Config object contains the write_document_declaration field. If you set to false it will skip the xml header.

I close this issue, re-open if needed. Marc-Antoine