This function returns the block heights closest to a provided date/time (time zone is GMT).
blockattime(con, targetdate)data.frame: the heights, the times and
the time differences (in minutes) to the provided date/time.
CONRPC, configuration object.
POSIXct, the date/time of closest block heights.
Bernhard Pfaff
Other UtilityFuncs: bkfee,
blockstats, date2int,
int2date, intMaxDay,
intMinDay, intRangeDay,
intRangePeriod, timeofblock,
txfee, txids,
txinids, txstats,
utxoage, utxotype,
utxovalue