fixed vusb variant of converter ps2usb

 * can be enabled by defining Makefile macro SERIAL_MOUSE_MICROSOFT_ENABLE or
   SERIAL_MOUSE_MOUSESYSTEMS_ENABLE.
 * Serial implementation can be chosen via SERIAL_MOUSE_USE_SOFT and
   SERIAL_MOUSE_USE_UART macros
 * UART configuration still has to be done in config.h: I added working clauses
   for both mouse protocols to ps2_usb's config.h

 * Both drivers use the interface defined in serial_mouse.h
 * They should work with any UART implementation (hardware/software UART)
 * The Microsoft driver is currently untested.
   The Mousesystems driver is confirmed to work.

- to support Adjustable keyboard(composite device?)

USB 6KRO with pseudo- or half- NKRO feature

Adding NKRO virtual dip-switch, using existing bit in keymap byte.

- without this fix wakeup often fails
- keyboard can wakeup once or twice but fails after that

- Command can force to enable NKRO even when boot mode
- After boot keyboard may be in boot mode due to BIOS' request

- NKRO is used only when keyboard_protocol = 1(report)

This takes the last, reserved bit there, but doesn't necessitate
a revision to the magic number because it doesn't alter byte order.
Add reference to NKRO virtual dip-switch to documentation.

Enhanced Backlight Support

To have full control of the backlight level.

Show correct function name for default layer set

Support for Lightsaber keyboard

Added NeXT keyboard converter