SoftwareSerial with ATTiny84 using ATtiny library

hilukasz
One thing to try:
Ensure that the MISO connection wire is as short (and fat) as possible:

(reply #74)

avrdude: please define PAGEL and BS2 signals in the configuration file for part ATtiny85
avrdude: please define PAGEL and BS2 signals in the configuration file for part ATtiny85

This is jusr a warning, just ignore it.