Map json nulls and optional fields to Option type

[kaashyapan]

@pimbrouwers Thanks for sharing this project.

Open to your comments.

Sorry I had to run the latest fantomas code formatter across the whole project. \ I'm not a big fan of the formatter but it was too painful without it.

[pimbrouwers]

Hi! Thanks for your work on this. I think the custom operators are also a nice touch, though you need to add examples in the docs before we can roll this in.

I also appreciate the splitting up of the tests. Good call.

I'd kindly ask you to roll back that running of fantomas. Aside from the core serializer, which is borrowed from Microsoft (as denoted by the comments), the F# was formatted how I prefer it. So let's make that fix before we dig any deeper into this.

[pimbrouwers]

How are things going on this?

[Numpsy]

I was going to say that the extra operators seem nice and the span stuff might be interesting, not sure how much effort it'll take to disentangle the multiple different changes and the formatting into separate changes though