Support Optional<primitive> in @JsonbCreator

[dansiviter]

Related to #121, new spec. doesn't mention OptionalInt, OptionalLong and OptionalDouble primitive wrappers. So small clarification to the spec. to permit these types.

[Verdent]

Each of the Optional types is not listed explicitly, but I would say this is covered by the following sentences:
If the parameter is any type other than Optional or its variations, then the null value is used. If the parameter is Optional or its variations, then the corresponding empty object must be used.

[rmannibucau]

+1 to clarify it, @dansiviter think you can feel free to PR the text clarification

[Verdent]

+1 Sure, I am not against it :-)

[dansiviter]

@rmannibucau Ahhh, that's some subtle wording, thanks for pointing it out. I suppose it is sufficient as it is and hopefully implementors honour it.