fix #302

the bug influences all args with the length 2, like id, fo, mm
fix test
Merge pull request #308 from zhiyelee/fixvariadic

fix #302
version bump
Merge pull request #309 from zhiyelee/2.5.1

version bump
all unknownArg
refactor
add tests

refactor the allowUnknown function
fix test
Merge pull request #310 from zhiyelee/uk

allow unknown function  #138