fancyopts: add early-options parser compatible with getopt()
The next patch will add a flag for strict parsing of early options, where
we'll have to parse all early options at once instead of processing them
one-by-one by dispatch._earlygetopt(). That's why I decided to hook
fancyopts().
All dispatch._early*opt() functions is planned to be replaced with this
function. But in this stable series, only the strict mode will be handled
by fancyopts.earlygetopt().