Optional relationship to Sized, Stream and other

[Michael Nascimento]

Hi folks,

After finally taking a look at the latest Javadoc and thinking about
it, I really think Optional could be better integrated with the
Collections framework and Lambda libs if it:

- Implemented Sized;
- Had a stream() method, allowing map to be called on the final result
only, for instance;
- Had a toSet() method

Regards,
Michael