Fixed double parsing on french computers where "125.23" wasn't parsed as double because it expected "125,23".
Two tests were failing because of this.
Used InvariantCulture to fix this instead of CurrentCulture.
extend the tests around the builder
work towards an additional arguments callback
Merge pull request #21 from do0om/develop

Fixed double parsing on french computers where "125.23" wasn't parsed as...
https://en.wikipedia.org/wiki/English_articles#Distinction_between_a_and_an

hth
Merge branch 'develop' of github.com:fclp/fluent-command-line-parser into develop
Merge pull request #22 from kjgorman/patch-1

an -> a
Merge branch 'develop' of github.com:fclp/fluent-command-line-parser into develop
AdditionalArgumentsCallback -> CaptureAdditionalArguments