* Adds separator.length() to calculation for desired width.
* Replaces use of term_width with options.term_width.
* Adds the comma and space separator to calculation for line-wrapping.
* removes redundant `.takes_value(false)`.
* changes Arg name to "list-languages" to be consistent with long-form.
* replaces unnecessary match statement with is_present().
* replaces unnecessary match statement on iter and uses unwrap_or()
instead.
* replaces for-loop with a call to join().
Connor Kuehl