implement a "speed" filter

[grandrew]

need automatic derivative calculation. This will greatly reduce complexity with "speed" types of plots:

#!/bin/sh
S=1; F=/sys/class/net/eth0/statistics/tx_bytes
while true; do
  X=`cat $F`; sleep $S; Y=`cat $F`; BPS="$(((Y-X)/S*8))";
  wget http://plotti.co/lock/plotticonet?d=${BPS}bps -q -O /dev/null
done

to

#!/bin/sh
while true; do
  wget  -q -O /dev/null http://plotti.co/lock/plotticonet_speed?d=`cat /sys/class/net/eth0/statistics/tx_bytes`bps
  sleep 1
done