Added support for ATTiny85 @1Mhz,, ATMega328 8Mhz

Library now supports following chip frequencies for RX
ATTiny85  @ 1Mhz, 8Mhz, 16Mhz
ATTiny84  @ 1Mhz, 8Mhz, 16Mhz
ATMega328 @ 8Mhz, 16Mhz