Support Compact<Option<T>>

[athei]

There is currently no easy way to compact encode a value that is wrapped in an option. We should add:

impl<T> {Encode, Decode} for Compact<Option<T>> where Compact<T>: {Encode, Decode} {
    ...
}

The compact encoding of the Option itself is unchanged from the non compact one: Prepending one byte to indicate none or some.

[thiolliere]

I'm not sure, this seems it wants to use the type Option<Compact<T>> instead.

Maybe it would be even better to have a real compact encoding for Option<interger> instead, like we could same as scale codec but with one bit used for the None/Some variant.

[athei]

Yes I think it makes total sense to have a smarter compact encoding for Option<integer>. In my current use case that would suffice as I have a integer type at hand.