Block._LARGEST_HASH not compatible with Dart2 #16
Description
The _LARGEST_HASH property on the Block-class doesn't work on Dart2 because integers have been limited to 64 bits. Potential replacement could be the new BigInt-class in Dart2. This may require refactoring.
static final BigInteger _LARGEST_HASH = (BigInteger.ONE << 256);
https://github.com/dartcoin/dart-bitcoin/blob/master/lib/src/core/block.dart#L73