Add ergodox_ez keymap to match Kinesis Contoured.

Add ergodox_ez keymap to match Kinesis Contoured.

This keymap attempts to match the Kinesis Contoured (aka Advantage) default
layout as closely as possible. See
http://www.kinesis-ergo.com/wp-content/uploads/2013/06/advantage_layout_win.pdf

Apart from the obvious mappings, this keymap also:

* removes the dual-purpose momentary layer/normal keys: Z, /, and Grv;
  because the author--coming from a Kinesis keyboard--finds the delays and
  accidental modifiers to be more disconcerting than helpful.

* puts Esc in the bottom left since there's no place for it in the top
  left to match the Kinesis.

* changes the bottom-right key into an L2 toggle since there's otherwise no
  way to get to L2.

* adds PrScr, ScrLk and Pause to the L1 keymap, down the left side, since
  they're present on the Kinesis but not available in the default
  ergodox_ez keymap.