XML Generator

[evgenyigumnov]

1. Implement "XML Generator" (generate function)

   pub trait TransformerTrait {
   fn parse(document: &Bytes, images: &HashMap<String, Bytes>) -> anyhow::Result<Document>;
   fn generate(document: &Document) -> anyhow::Result<(Bytes, HashMap<String, Bytes>)>;
   }

   Look at json module like example

2. Units test requered for this new feature (looks at tests in json module)