* Keymap architecture
** Keymap definition module
   The keymap definition module defines:
*** The key mappings used by a keymap
*** The virtual devices required by the keymap
    This includes definitions for LED's and I/O lines, including their initial
    states, and default I/O operations such as toggle, pulse, etc.
*** Function hooks used by the keymap.
    Specifies which functions are used for operations such as key scanning, I/O,
    special keybindings, etc.

  Any special functions or logic required by the keymap are also defined and used in the module.

** Keymap definition API
*** mapping keys
    #include "asdf_keymaps.h" 
**** asdf_keymaps_add_map() - called from 
     Assigns a specified keymap matrix (ptr to FLASH) to a given keymap and modifier type.
*** adding virtual devices - called from keymap setup routine
**** asdf_virtual_init()
***** Clears the virtual device table for the keymap
***** initialize first entry in virtual device table to NULL
**** asdf_virtual_add_device()
***** Accept a virtual device code, a physical device code, a default function, and a default initial value, and create a new entry in the virtual device table.
***** increment the virtual device table pointer and set next (last) entry to NULL

* Eliminate keymaps table and instead have table of keymap init routines with MAX_KEYMAPS entries
* keymap setup routine adds maps for each modifier to the keymap, now only rxcxMODIFIERS instead of rxcxmodifiersxkeymaps
* remove the keymap index from the add_map() call.
* select_keymap() will call setup routine for the given keymap.
* Each keymap sets its own num_rows and num_columns, per matrix for each modifier