Add Timer to display
Update texts

Change the term `frame' to `packet'
Change term NACK to NAK
Add independent error assumption
Change term Frame error rate to Block error rate
Change term send to transmit
Merge branch 'new-look'
Change how a receiver works

A receiver now sends NAK after receiving an erroneous packet,
instead of discarding it and delay NAK until an error-free
packet arrives.
Improve spec readability
Merge branch 'node-reform'

Change the way a node treats erroneous packets and
improve spec readability.