Improve documentation.
Fix
//! The type of the field gives the kind of argument:
//!
//! Type | Effect | Added method call to `clap::Arg`
-//! ---------------------|-------------------|--------------------------------------
+//! ---------------------|--------------------------------------|--------------------------------------
//! `bool` | `true` if present | `.takes_value(false).multiple(false)`
-//! `u64` | number of params | `.takes_value(false).multiple(true)`
+//! `u64` | number of times the argument is used | `.takes_value(false).multiple(true)`
//! `Option<T: FromStr>` | optional argument | `.takes_value(true).multiple(false)`
//! `Vec<T: FromStr>` | list of arguments | `.takes_value(true).multiple(true)`
//! `T: FromStr` | required argument | `.takes_value(true).multiple(false).required(!has_default)`
//! .required(false)
//! .validator(parse_validator::<f64>)
//! .short("s")
-//! .long("debug")
+//! .long("speed")
//! .help("Set speed")
//! .default_value("42")
//! ```
