Add from_optional helper method to Option

[rksouthee]

I've ran into a few scenarios where I need to convert from typing.Optional[T] to rusty_results.Option[T] and was wondering if we could add a helper function that would create an Option[T] from an Optional[T], something like Option[T].from_optional.

[check69]

Nice suggestion, we will add this in the next version. Thanks!

[AlejandroCabeza]

Resolved with #20.