Changes to Atreus and Ergodox EZ Dvorak 42key layout (#1997)

* importing 42 key dvorak layout

* added comment for build instructions

* adding atreus dvorak 42 key layout

* added readme

* add readme

* build instructions

* additional MEH shortcuts

* added shifted symbols on symbols layer

* working extra symbols on COMBINED layer

* bring atreus layout inline with the ergodox one

* add necessary macros

* working ls macro

* added more shell macros

* added screen rename / screen number macros

* add ctrl-a key in shell-nav to use screen more easily

* added shell screen layer

* assign screen switching macros to screen layer

* define all screen switching macros

* more screen-related shortcuts added on shell screen layer

* change shell nav bottom right row to match base layer (backspace / delete)

* remove some mappings on SHELL_NAV layer as they are now in the screen layer

* added more screen macros

* changes to COMBINED layer (pipe on the right) and modified shell nav

* moved pipe/backslash to then right

* documented SHELL_SCREEN layer

* put backspace/delete on SHELL_NAV layer

keyboards/ergodox_ez/keymaps/dvorak_42_key/README.md

@@ -14,4 +14,5 @@ Layers
 * KEYSEL: similar to KEYNAV, except for shift-selection
 * COMBINED: this is a layer that combines numbers, brackets and special characters. !@#$%^&*( can be type by shift+COMBINED+1/2/3/etc..
 * MOUSE: mouse navigation, as well as browser tab-left/tab-right shortcuts
-* SHELL_NAV: Linux Bash shortcuts (move forward/backward in command line, move between screen windows, Ctrl+C, recall last argument, etc
+* SHELL_NAV: Linux Bash shortcuts (move forward/backward in command line, Ctrl+C, recall last argument, etc
+* SHELL_SCREEN: Linux screen (run multiple terminals in one window) shortcuts such as open new tabs, switch between tabs