stephengrier's TADA68 layout

This layout mostly replicates the default ANSI layout of the TADA68 but with a few modifications to suit my tastes.

The modifications from the default keymap are:

• Replaced capslock with a second function key
• Swapped the left ALT and Win keys to be more like the Mac layout
• Added an arrow key cluster on the IJKL keys
• Fn+x toggles backlight breathing mode

With this keymap backlight breathing mode can be enabled/disabled with Fn+x. This is not supported at all in the default keymap.