Unify signature and error handling in parse_long, parse_shorts.
Unify signature and error handling in parse_long, parse_shorts.

kenwilcox/docopt,Zearin/docopt,snowsnail/docopt,devonjones/docopt,crcsmnky/docopt,docopt/docopt,benthomasson/docopt,wkentaro/docopt,jagguli/docopt