Add support for dual long options when no short option

[shadowspawn]

Problem

#2270 throws an exception for unsupported option setups. This is picking up more variations than expected, and use of a short-ish form is more widespread than assumed (despite being at odds with the documented usage).

• multiple character short option: Return support for multiple character short options #2307
• dual long options: Throw for unsupported option setup #2270 (comment)
• triple dash: GNU-style triple-dash option (---gnu-style-hidden-option) no longer work in 13.0.0 #2309

In particular, people want to have a multi-character shortish option.

Solution

The high level goals are still to restrict usage to supported formats, and follow standard conventions.

As per #2307 (comment)

Short version: my latest thinking is to add explicit support for a short-ish option, but with double-dash rather than single dash.

Long version

There are strong conventions for short options (POSIX) and long options (GNU). I am uncomfortable about supporting a third and non-standard variation with multi-character short option.

But I appreciate the author desire for a more memorable short-ish option than a single character.

Adding explicit support for a double-dash short-ish option feels like a more pure approach still offering the key benefit. e.g. --es, --ecmascript <year>

There are no new behaviours that need to be decided or described for the short-ish option, and it is full featured. Can you embed option value with a short-ish option? Of course, --es=2018. Can you combined short and short-ish options in a single argument after a single dash? Of course not.

So:

• Multiple character short option: no, conflicts with standard posix and incomplete (no embedded value support). Use double dash instead. See next item.
• dual long options: yes, add support for this as the intended format for "shortish" option like --ws, --workspace
• triple dash: no, rare

ChangeLog

• add: support for a pair of long option flags to allow a short-ish flag, like .option('--ws, --workspace')