Fix Example Checks

[sommersoft]

During validate_contents, the check to make sure each example is prefixed with the library name, the repo's name was used. The rfind() was set to look for the first _, which resulted in errors when the repo had an extra underscore beyond CircuitPython. Example: Adafruit_CircuitPython_Thermal_Printer gave a lookup string of printer.

This changes the the rfind() to look for CircuitPython_ instead, ensuring that the whole library name is captured.

Also fixed a couple latent bugs from the refactor, wrt to the -v command line flag.

[makermelissa]

Looks good to me.