Function parse_level 

pub fn parse_level(
    input: &str,
) -> Result<(LevelFilter, Vec<TargetLevel>), String>

use log::LevelFilter;
use simple_log::level::parse_level;
let input = "off";
assert_eq!(parse_level(input).unwrap(), (LevelFilter::Off, vec![]));

let input = "debug";
assert_eq!(parse_level(input).unwrap(), (LevelFilter::Debug, vec![]));

let input = "info";
assert_eq!(parse_level(input).unwrap(), (LevelFilter::Info, vec![]));

let input = "warn";
assert_eq!(parse_level(input).unwrap(), (LevelFilter::Warn, vec![]));

let input = "error";
assert_eq!(parse_level(input).unwrap(), (LevelFilter::Error, vec![]));

let input = "off !!!";
assert_eq!(parse_level(input).err().unwrap(),
r###"Failed to parse level:
off !!!
   ^
"###);

let input = "warning";
assert_eq!(parse_level(input).err().unwrap(),
r#"Failed to parse level:
warning
^
attempted to convert a string that doesn't match an existing log level"#);


let input = "info,";
assert_eq!(parse_level(input).err().unwrap(),
r#"Failed to parse level:
info,
    ^
"#);

let input = "error,app=off";
assert_eq!(parse_level(input).unwrap(), (LevelFilter::Error, vec![("app", LevelFilter::Off).into()]));

let input = "debug,app=error,";
assert_eq!(parse_level(input).unwrap(), (LevelFilter::Debug, vec![("app", LevelFilter::Error).into()]));

let input = "debug,app=error,filter_module::app::ctrl=error,app::launch::c123onf=info";
assert_eq!(
parse_level(input).unwrap(),
 (LevelFilter::Debug, vec![
  ("app", LevelFilter::Error).into(),
  ("filter_module::app::ctrl", LevelFilter::Error).into(),
  ("app::launch::c123onf", LevelFilter::Info).into(),
 ]));