Add KDL parser/generator

[evgenyigumnov]

1. use crate:

kdl = "4.6.0"

2. create kdl.rs in "lib/src"

3. implement this trait

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

just check html.rs for example

example of KDL document:

document page_width=210.0 page_height=297.0 left_page_indent=10.0 right_page_indent=10.0 top_page_indent=10.0 bottom_page_indent=10.0 {
    elements {
        header level=1 "Employee Report"
        image src="data/logo.png" title="Some title" alt="Some alt"
        paragraph {
            text size=8 "blabla bla bla blabla bla bla blabla bla bla blabla bla bla bla"
            text size=8 "other text"
        }
        list numbered=true {
            text size=8 "First item"
            text size=8 "Second item"
            list numbered=true {
                text size=8 "3rd item"
                text size=8 "4th item"
            }
        }
        header level=2 "Second header"
        table {
            table_header width=150 {
                text size=8 "Name"
            }
            table_header width=50 {
                text size=8 "Salary"
            }
            row {
                cel {
                    text size=8 "John"
                }
                cel {
                    text size=8 "1000"
                }
            }
            row {
                cel {
                    text size=8 "Tommi"
                }
                cel {
                    text size=8 "3000"
                }
            }
        }
        paragraph {
            text size=8 "Some link: "
            link title="http://example.com" url="http://example.com" alt="http://example.com" size=8
        }
    }
    page_header {
        paragraph {
            text size=8 "Page header"
        }
    }
    page_footer {
        paragraph {
            text size=8 "Page footer"
        }
    }
}