blink1-tool should allow '0' repeats for blinking indefinitely

[todbot]

e.g. both of these should result in blink(1) flashing red for eternity:

blink1-tool --playpattern '0,#ff0000,0.2,0,#000000,0.2,0'

blink1-tool --rgb FF0000 --blink 0

This does break the philosophy of blink1-tool always eventually exiting, but we'll allow it in this case.

[todbot]

A work-around for now is to set the number of repeats when using --playpattern:

blink1-tool --playpattern '-1,#ff0000,0.2,0,#000000,0.2,0'