Allow retrieving Caps/Num/Scroll Lock Status

[SukkoPera]

This patch applies (mostly) cleanly to the sources included with Arduino 1.8.13 and seems to work well for the purpose, while sporting a simple interface.

I think it should really be considered for inclusion upstream.

[phuse]

was just looking for exactly this since I'm hacking together a numerical/macro keyboard

[PJ789]

I can vouch for this patch too. It is working well here against current keyboard code. There is a dependency on the HID library that means I'm hesitating to offer it as a pull request. Perhaps it can be made more specific to the keyboard library without unintended side effects on the HID library..?

[PJ789]

Two pull requests created to incorporate this feature;

1. Keyboard library pull request 61

which depends upon

2. ArduinoCore-avr library pull request 446

regards Pete