use Data.Word to generate max 2^64-1
use Data.Word to generate max 2^64-1

but nimrod denies too big unsigned int so suppress it to 2^63-1

Signed-off-by: Akira Hayakawa <4e4688318b48ded9892634f64b2ffe50a6dee1f6@gmail.com>

zchee/msgpack-nim,zchee/msgpack-nim,akiradeveloper/msgpack-nim,rogercloud/msgpack-nim,akiradeveloper/msgpack-nim,rogercloud/msgpack-nim