expandOptionsShortcut

• Overload of docopt that accepts a compile-time parsed descriptor. *
• This avoids reparsing the documentation at runtime when a string literal
• was available at compile time. Semantics are equivalent to the string
• overload. Expand every [options] shortcut in pattern with the options declared in the document that do not already appear literally in the pattern.

Shared by both docopt overloads so the expansion cannot drift.