Lots of development

* Add ability to send the ATtiny a different CDC text string

* ATtiny startup now does a few 50% duty cycle blinks.

* Add -s parameter to pibus:
  -s <string>  Send extra string to IBUS at startup

* Add long-press Prev/Next to do CTRL Left/Right keys

* Request Time & Date if they aren't seen for 15 seconds

Signed-off-by: PeteAU <pete@classiccomputing.info>