Add an off-heap Option

[adam-wyluda]

It would work like one-element off-heap array. Option.empty would be just a null reference, otherwise it will point to address containing value of this Option.

The use case for this class is return value of some off-heap collection methods, such as find or get in Map.

[adam-wyluda]

Also the benefit of having an Option as a return type for methods, is that it can dereference primitive type values to memory instead of returning them directly, which effectively allows us to have null references of the primitives.

[densh]

Sounds good to me.