Adjusted Atreus KEYMAP() function.

Adjusted Atreus KEYMAP() function.

This change adjusts the KEYMAP() function to provide a more visual representation of the key positions on the keyboard. Previously, keymaps have been defined directly using arrays for the Atreus keyboard. While this works, it doesn't utilize the helpful KEYMAP() function at all to allow the user to visually position the key codes for ease of editing. See the Ergodox-EZ KEYMAP() function and layouts for a great example of how this can work.

This change should not break any existing Atreus layouts. At the time of this commit, there are two existing layouts for the Atreus board, and neither use the KEYMAP() function.