Issue 44 - Simple implementation of varargs for lists

I developed this little feature for version 2.4.2 because it'd make my team's (and hopefully many others) work a little bit easier every day.
It overloads a `withSomeList(List<Foo> value)` method by a varargs variant (`withSomeList(Foo... values)`) using the generic type of that List (maybe there is need for a fallback when no generics are used). An (modifiable) ArrayList is used as implementation.
See also: [Issue 44](https://github.com/mkarneim/pojobuilder/issues/44)