Use StateT from F#+

[gusty]

I want to see the impact of using a StateT from F#+

If it makes sense we can eventually merge it but that's not the main motivation to me.

[gusty]

Note that:
<??> sprintf "uint16be: failed at %i"
is equivalent to
</catch/> (fun (ParseError (p, _) ) -> throw <| ParseError (p, Other (sprintf "readString failed at %i" p)))

which would be the "standard way", however it's too long. Maybe it's a consequence of the current ParserError design.

[smoothdeveloper]

@gusty, if using </catch/> in <??> implementation, what would it look like?

[gusty]

Good point !
It would look like this.