Changes in version 1.19:

A new value has been added to Has_arg; yme = 'yes but maybe empty'.
It allows an option to take the empty string as an option-argument.
'yme' was added for completeness, but its use is not recommended.

'typedef' is used again in the C version (carg_parser.h).

The syntax of options with an empty argument has been documented in chapter
'Syntax of command-line arguments' of the manual.
