Added support for grouping boolean options by short name

[zefir-git]

Flags (boolean options) like -a -b -c can be grouped like -abc (in any order). Only works for flags/booleans and only for short options.

Example:

new Program("cmd")
    .option("-f, --foo", "foo")
    .option("-b, --bar", "boo")
    .option("-B, --baz", "foo")
    // …

The flags can be set to true like so:

cmd -fbB
# equivalent to:
cmd -f -b -B

When reading the parsed flags, they are still read separately:

auto foo = args.flag("-f");
auto bar = args.flag("-b");
auto baz = args.flag("-B");