Bluetooth Keyboard support

[finzic]

It would be great to add a feature so that Charon becomes a 'hub' for BT keyboard-connected devices.
Instead of having 1 BT keyboard connected to N devices, you would have 1 normal keyboard connected to N devices through Charon, and let the raspberry pi handle BT connections to the 'target' hosts.
One benefit would be that you could use your favourite keyboard even if it does not have any BT support.
Another benefit is that... your normal keyboard would not leave you alone discharged out of nowhere :)

[ddrcode]

Hey - thanks for the idea, @finzic. I would split it into two separate features:

1. Charon as BT keyboard (with regular keyboard plugged to it)
2. Charon as BT keyboard switch (Single Charon, multiple hosts)

That, naturally, expands to two related ideas (not in your proposal)

3. Support for BT keyboards on Charon side
4. The Consequence of 2 - Charon as Keyboard switch in general (wired or BT).

I've been thinking a lot about 4 (wired version), actually, so I completely buy the idea. Doing it wired way would require extra hardware - as RP has only one port that con be configured as USB gadget. I wonder whether BT could simplify it. I have zero experience programming BT devices, so it's unknown to me. Do you have some?

Idea 1 feels a little bit strange to me – Charon is rather a "stationary" device, so connecting it to the host via BT feels bit odd. Although I hear about solving charging problem with it. At first it feels to me like 1 makes a lot of sense when combined with 2. I am happy to experiment. Some of my keyboards actually support BT, but I have always been using them wired.

Would you be interested to contribute to that? Even if not on Rust side, there is a bit of research to be done - mostly around RP switching between hosts and - in general - RP as BT HID device.