format of input .json to t8n

[winsvega]

ethereum/evmone#1078

apparently we export dec fields as dec

"currentDifficulty" : "131072"

and it would be better to follow the standard. of exporting all dec values as hex. "0x020000"
but as far as I know geth t8n do not accept even padded hex so any leading 0 is truncated to "0x20000"

we shall enforce t8n inputs to be of geth hex format eg: "0x1" "0x0" "0x1ac"