Add DecoHelper
Add helper for statistics. Record measurement error (of measured distance).
Fix bug when sending fails
Implement a simple filter for estimating distance
Implement Lateration tracking algorithm
BaseWirelessPhy: do not switch to TX mode automatically when receive notification from upper layer; switch to TX mode automatically when receive packet from upper layer (if neccessary). CCA is only valid if in RX mode.
Implement interframe spacing IFS