Modifier tap hold in keyboard toml

[hariseldon78]

This pull request closes issue #221.

I have been able to test the MTH(A,LShift) and it works correctly, but for some reason the TH(X,Y) is not working yet: has it been tested before? I see that Via does not have a binding for the TapHold.

I used all caps for MTH and TH for consistency with the other Layer actions, and i used the ordering , for consistency with WM and LM.

[hariseldon78]

i also fixed Lgui and Rgui to LGui to RGui, let me know if that was a bad idea.

[HaoboGu]

I see that Via does not have a binding for the TapHold.

Yes, via/vial supports only ModifierTapHold and LayerTapHold.

Only basic keycodes are supported in normal TapHold:

rmk/rmk/src/action.rs

Lines 46 to 49 in 7970200

	/// General tap/hold action. Because current BaseAction actually uses at most 7 bits, so we borrow 1 bit as the identifier of general tap/hold action.
	///
	/// Serialized as 1|BasicAction(7bits)|BasicAction(8bits).
	TapHold(Action, Action),

I have a plan to use 32-bit keycode, which would eliminate this limitation in the future.

[HaoboGu]

Thanks very much!