Convert an Ethereum blocknumber to a timestamp
if the block number has yet to occur it will return a simple prediction
of the timestamp achieved by adding 12 seconds for every block between
the current requested block
Convert a timestamp in the form YYYY-MM-DD HH:MM:SS
to an Ethereum block number.The first block to occur
after or at the timestamp will be returned.
if the timestamp has yet to occur it will error.