upgrade yaserde to 0.12

[Cyrix126]

Do not merge yet
Three breaking changes:

parameter namespace is now namespaces and can include multiple namespace.

#[yaserde(prefix = "tns", namespace = "tns: http://example.com")]
#[yaserde(prefix = "tns", namespaces = {"tns" = "http://example.com"})]

This PR needs to be edited to take into account that multiples namespace must be included in one parameter.
Using this PR at the current state with multiple definition of namespace will generate incorrect code.

field attribute needs to have a boolean value instead of just being present.

    #[yaserde(attribute, prefix = "tns", rename = "id")]
    #[yaserde(attribute = true, prefix = "tns", rename = "id")]

name of encoding is now UTF-8 instead of utf-8.

        let s = r#"<?xml version="1.0" encoding="utf-8"?>
        let s = r#"<?xml version="1.0" encoding="UTF-8"?>