* Use TAPPING_TERM constant (and redefine value to 200ms)
* change TAPPING_TOGGLE to 2 to require two taps to lock in layer 4
* add support for Shift-Command 3/4/5 key combinations that are used in
macOS Catalina
* avoid false positive tap detecion for RMOD3 when the whole sequence of
pressing RMOD3, tapping another key and releasing RMOD3 took less than
TAPPING_TERM milliseconds.
* replace SEND_STRING with tap_code()/tap_code16(), saving ~860 bytes in
compiled firmware size.
This is a Neo2 inspired layout that is meant to be fully usable on
MacOS when used with the default US QWERTY/ABC Extended keymap.
Neo2 layers 1-4 have been almost fully implemented in hardware.
Layers 5 and 6 (greek and mathematical symbols) have been left
out for now as most of them aren't available on the default
keymaps.
Layer toggling for layer 3 on the right hand side utilizes a
tap-toggle approach that is a combination of MO & LT macros.
This is required to allow sending Y when tapped, @ when tapped
while the SHIFT modifier is active and support momentarily
toggling the layer while the key is held.
