Jinja compability: Functions with a trailing comma

[joshuataylor]

Description

The following should be supported 😢 😬 :

        {{basic_function('hello', 'world') }}
        {{basic_function('hello',
        'world') }}
        {{basic_function(
        'hello',
        'world') }}
        {{basic_function('hello',  'world',) }}

        {{basic_function('hello', 'world') }}
        {{basic_function('hello',
        'world') }}
        {{basic_function(
        'hello',
        'world') }}
        {{basic_function('hello',  'world',) }}"#,

Test Replication:

fn basic_function(_state: &State, arg_one: String, arg_two: String) -> Result<Value, Error> {
    Ok(Value::from(format!("{} {}", arg_one, arg_two)))
}

#[test]
fn test_functions() {
    let mut env = Environment::new();
    env.add_function("basic_function", basic_function);
    env.add_template(
        "demo.html",
        r#"
        {{basic_function('hello', 'world') }}
        {{basic_function('hello',
        'world') }}
        {{basic_function(
        'hello',
        'world') }}
        {{basic_function('hello',  'world',) }}"#,
    )
        .unwrap();

    let tmpl = env.get_template("demo.html").unwrap();
    insta::assert_debug_snapshot!(tmpl.render(&()).unwrap());
}

Right now it throws this:

thread 'test_functions' panicked at 'called `Result::unwrap()` on an `Err` value: Error { kind: SyntaxError, detail: Some("unexpected `)`"), name: Some("demo.html"), lineno: 8, source: None }

Not sure if it should be supported for backwards compatibility or not..