BigInt bool assign

[bearophile]

Paul D. Anderson:

>  From std.bigint docs:
> 
> "All arithmetic operations are supported, except unsigned shift 
> right (>>>). Logical operations are not currently supported."
> 
> Maybe when support for logical ops are added support for booleans 
> will be introduced for consistency.

Don has closed my tiny enhancement request, he doesn't want to change that.

Bye,
bearophile